France / Spain with 10 and 7 year olds in July.

I wouldn't worry about your lack of French. You will cope. Your Spanish skills will be of some assistance, I imagine. Look at it this way: If you greet people in French, then switch to Spanish, you won't be expected to discuss US politics!

I haven't driven in Europe, so take that into consideration.

For the Paris-Barcelona leg you are looking at about 13 hours for the night train (with a transfer around 8 AM) vs. 6-1/2 hours for a fast day train. There's a 2:07 PM departure that sounds a lot more attractive to me than spending all night on trains, though I understand the theoretical attractiveness of a cozy nighttime rail trip. It would be good if you could find some information about that particular night train. Some rail lines are much smoother than others, making the ride a lot more comfortable.

For the Madrid-Santiago de Compostela leg, ViaMichelin estimates a driving time of 6:47 without any stops. The train takes between 6 hours and 6:20 in most cases and would avoid the hassle of navigating out of the large city. If I were certain of my travel dates I'd consider snapping up promotional train fares as soon as the tickets go on sale, but those would be completely non-changeable/non-refundable. On the other hand, the driving route takes you pretty near Segovia (Aqueduct alert! Plus interesting architecture).

I fiddled around with the map and couldn't figure out a way to fit in Bilbao. If you didn't have to be in SdeC on a specific date, I'd offer the possibility of driving Madrid-Bilbao-SdeC, but that's not going to work. If you could convince the Madrid family members to meet you in Galicia...

It is often mentioned here that renting in one country and dropping in another usually incurs a large one-way surcharge, but it's certainly worth checking with a few car-rental providers to verify that it would apply in this case.

Vueling has a 6-1/2 hour connection from Vigo to Lyon (changing in Barcelona). It's currently available for July 24 at $97. There's a SdeC departure that makes the same connection in Barcelona, but the trip is one hour longer. It's currently $118. I don't know whether you've previously been to Vigo. I found it far less attractive than SdeC, A Coruna and Pontevedra.

If you just want a non-stop flight to Barcelona, you can get those tickets for about $60 or less at the moment. Or you could take Vueling's non-stop to Paris (9:45 AM, $70). Skyscanner.com was my source for this flight info.

I'm confused about the duration of your trip. Is July 11 the day you fly out of Miami or the day you arrive in Paris? And are you flying home on July 26?

I would definitely fly from Paris to Barcelona. Night trains are not very comfortable and will eat up way too much time.
You won't have any trouble with the language in Paris. Just remember to say "Bonjour" and "Merci" and you'll be fine.

You have a pretty good plan. However, check the auto rental if you plan to drop a vehicle in another country from where you rented the car. It may include some very hefty fees.

I have visited Spain several times and think two nights in Madrid is not enough, but I know you have limited time.

We recently did a Douro River Cruise out of Porto, Portugal and loved it, which I know you will not be doing. However, we did visit Santiago de Compostela on a day trip and loved the city. Galacia is an interesting area and a bit different from other parts of Spain.

When my kids were young, we traveled in Europe and I always tried to have the somewhat educated on where we were going. My oldest was 11 when we started traveling and she remembers all the trips and my explaining the history of places we visited. She has a masters in history and loves it. My son was 5 and he doesn't remember that much of where we visited prior to age 10. Still, you can make it fun for them. They might get tired of museums, but my kids were in awe of some things, like the Sistine Chapel, St. Peter's, the gondolas in Venice and the Eiffel Tower.

Enjoy your trip

Awesome, thanks everyone for the info. The family from my side is from Galicia and that is where we are having a family reunion. On my wife's side they are from Madrid which is why we are spending several days there even though we both have been multiple times just not recently. My main concern was trying to squeeze in too much but sounds like I am not pushing it with a 2 day buffer. I plan on using those 2 extra days to find kids only activities or day camps. My daughter is in a flamenco program at her school so my aunt over there is looking into a possible flamenco camp for a few days. My son pretty much refuses to learn spanish so maybe an immersion day or two will do him some good. He tends to know a lot more than he lets on.