Strategy to talk BIL into packing light

Honestly, it sounds like it's his problem not yours, although I don't see how he can carry all that luggage and find room for it in his hotel room.

You cannot. Packing light is learned behavior. If the problem last year didn't have an impact what makes you think that there is anything your can say that would have an impact. The only thing you can change is your attitude and just adjust that this trip will move slower. I have a similar sister-in-law. With nose high in the air, "It is uncivilized to be seen in the same clothes for more than eight hours." Been down that road for years -- no effect.

PS -- At home she only wearing a nightgown one time so have to have one for each day.

We've done carry on for years because of all of the benefits. But, in this case, I think I'd back off. What I would do is tell him you want him to be comfortable on this trip. Mention how unfortunate it was that they were delayed on a previous trip and just say that to reduce any risks on this trip, it would be wise to have separate reservations for all train tickets, etc. for each of you. If anyone is detained in route due for any reason (luggage, illness, etc.), two or three of you could still move ahead, depending on the severity of the reason.

And, personally I would be happy that he's planning to change clothes and cares about other people if he's that sweaty.

I have a friend like that. She took the biggest suitcase to Greece in June. I didn’t wait for her nor did I help her watch her baggage while on trains. I’m done with it all.
She tripped over it once on a cobblestone street. She fell flat on her face. I had a hard time keeping my mouth shut.

Congratulations to the Niece!

We travel light and plan on a cafe afternoon every three or four days for laundry, and making the next set of plans.

You can not do much for the BIL..... but you can investigate laundry services where you will be staying... Hopefully staying in one place for several nights at time... More laundry costs, fewer bags checked. 6 outfits, three days, laundry every third day. Or, you can arrange to ship a box of three days clothes to the first/an early hotel at which you will be staying. Delayed luggage - no problem... This might also allay his anxiety about needing to overpack since things will be waiting for him. Mail stuff home.... Choose your pain.

We travel with my cousin and her husband. Great fun, let me plan all, never complain, very flexible, but they over pack. She also needs a clean nightgown every night. Well, after last summer’s trip to Poland and traveling by train, carrying their suitcases up and down staircases, etc., they finally said to us - we have to pack lighter next trip. We haven’t stayed in one hotel that didn’t have laundry service, which they have used. My point? Sometimes people have to realize light packing is the way to go on their own. Is it a drag for us light packers, yes. Would it be enough to not travel with them again, no.

IME, if you convince him to pack light, he'll just complain that you wouldn't let him bring what he needed. But it isn't just his problem if it slows you down.

The only good suggestion I've heard of, is to have him test- pack like he wants and have him walk around your town, up and down stairs, on and off city buses etc.

The only good suggestion I've heard of, is to have him test- pack like
he wants and have him walk around your town, up and down stairs, on
and off city buses etc.

I agree! It's not clear from what you've told us so far about this lovely, luggage-laden gentleman; has he traveled abroad before? He may not understand what a different animal it can be, what with lots of steps and stuff like elevators, working escalators and air conditioning not being a given o'er there. Short of bringing a sherpa, test-climbing a couple muggy flights of stairs and trucking around the block a couple of times with his luggage - in July (what month will you be traveling?) - might cure the disease.

Then again, how much moving around will you be doing with your bags?

So he has kindly explained about the clothes (laundromats really are wonderful things) but what's with all the shoes?!!!

Test packing and carrying is a great idea.
Plan B - scare him about the possibility of lost luggage. Hence, the need to do carry-on only.
Plan C - cost of excessive luggage and weight restrictions by the airlines.
Plan D - shopping for things you need in a foreign country can be a fun experience.
Packing cubes can help with visualization.

Touchy situation. Be straight up front, Offer to help him do a practice packing as you would do it. If he packs his way, it is not just his problem because he is now one of your travel partners and he will disrupt this fantastic gift trip you are giving your niece. Tough love is the answer. Good luck and enjoy your trip.

Last spring he and his girlfriend were delayed by more than two days when travel plans snafu-ed, as they do, and he was unable to be flexible due to his luggage

Make it clear you will be 'moving on' and not waiting for luggage to catch up ( or whatever the problem was)

Be sure he understands he will be his own 'porter' Unless you stay at a big US chain hotel it will be unlikely there will be porter service available. If Venice is part of the trip, find photos of the bridges and all their stairs to negotiate. If that does not do it nothing will.

Most hotels will have small elevators. One I was at had room for two people ( strangers may have felt uncomfortably close) or one person and a rolling carry on.

Good luck, and to paraphrase our host "keep on traveling, and don't be delayed by the overloaded"

In all fairness to your BIL, it sounds like you want everything your own way, with no room for compromise. Your way or the highway, as it were. Exactly how fast are you moving? Has there been any discussion about the itinerary amongst you or has this been fixed and set by you? Why must he only bring a carryon? Why would a 24 or 25 inch suitcase be ruinous to your vacation?

It seems obvious that you and your BIL have very different approaches to vacationing. Perhaps sitting down for a frank discussion about expectations on BOTH sides; reviewing the itinerary and modes of travel, with an eye to compromise, might help minimize hurt feelings and/or frustration on the trip. Maybe something as simple as telling him that he has to carry all of his own bags will help. And perhaps plan for the contingency of delayed checked luggage- the rest of you carry on and he can catch up with you when he can. And please, if he is kind enough to pare down his packing, make sure that you have identified, in advance, laundry facilities at all of your stops so the poor man can have the fresh clothing that he needs.

Would you care to share what methods of transportation you are planning to use on this trip and how often you are changing locations? If cars or taxis are part of the equation, the amount of luggage will make a difference. Friends who were using a car brought all the suitcases together and tried fitting them in one of their cars roughly the same size - that changed the luggage travelers were planning to bring.

I want to thank everyone most sincerely for each and every one of these replies. Together, they have given me a lot to think about. Your experience is invaluable.

I have given particular thought to the idea that I might be overthinking this. :) It may be possible to arrange more flexible travel plans than the ones I am used to so we can accommodate BIL. His need for fresh clothing is reasonable, but I'm hoping more laundry and less luggage might be the solution. That said, we can also work through some alternate systems such as car vs. train travel.

Sitting down comparing travel styles is an excellent suggestion. He's such a lovely person as well as our niece's Dad that I really don't want to do the trip without him.

I will update you all on how this shakes down. Thanks again for your varied and valuable suggestions.

We have relatives like him. They bring more to our house for a weekend than we take on six weeks trips. Several changes of shoes a day.When they traveled in Europe with friends each couple had to rent their own car.
The car is your weapon! Show him the diagrams on AutoEuope showing the cars and the amount( small) of luggage that can be stowed. And if using trains, tell him his bag has to fit above the seat and that there are no porters to help him.

You can’t. The best you can do, at the risk of damaging your relationships, is to make it clear their baggage is their responsibility. And then, just like with little kids, you’ve got to stick to your commitment, even if it means there are uncomfortable situations and totally avoidable consequences.

Your trip could get ruined two ways, oh boy! You get stuck tending their luggage or they’re mad at you for refusing to attend their luggage.

https://www.youtube.com/watch?v=d5MsEC8PgFc&fs=1
Here's a video about dragging your huge bags around Venice, just as an example, that you could show him.
I know you're going to France, but it illustrates how hard it is to move about with big bags.
He could still check a bag.
He could bring two pairs of shoes so he could alternate, and some sandals that can be scrubbed if sweaty, like Tevas or Keens.
The best advice I've seen here is for everyone to have separate bookings for trains, etc.
If someone else is delayed because of their luggage issues,then the rest can go on ahead.
I wouldn't help him haul his bag (?bags?) once you're there, if you have tried to give him the best possible advice before you leave.
Sounds cruel, I know.
Have you had him plan any of the trip; I think it would be a good idea.
What about your niece? Can she influence him?

(I'm pretty sure I'll be the 25 inch suitcase & tote as in the video when I go to Venice) but I have an apartment with no bridges [unless there is a vaporetto shut down] and not steps)
I also think aiming for a 24/25 inch bag & 25L back pack is not unreasonable. Go ahead and do trains with it. Consider short let apartments as there seem to be at least 4 of you. Ensure they have washing machines.
If a car is a must, then you need to look at a larger car. Accept it. Realistically, even 4 carry on suitcases plus 4 adults is going to need more room than a Punto.

Some folks only learn from personal experience. And some never learn. You can't be your brother-in-laws keeper. And who knows what is really right for a person's specific needs.

There are good friends I enjoy traveling with and good friends I avoid traveling with. We all have difference paces and internal clocks. I have retired friends who still get up before dawn's early morning light and I have friends who are the very slow starters where my lunch is their breakfast. Travel with Goldilocks friends (relatives) or just realize that they will not comfortable change just to keep you happy.