England vs Ireland vs Scotland for a multi-generational trip

Given the time you have it would be easy to visit both England and Scotland as there’s very regular trains between the two, though for 8 travellers I appreciate it may be expensive.

I guess it also depends where your MIL wants to go: does she want to visit ancestral homes, or just see general sites? What does the rest of your clan want to see?

If you only wanted a cursory feel for Scotland and England, then 7-10 days would be sufficient. Depending on what you wanted to see, unless it's in the border area, then I'd stick to one country as 7-10 days isn't really that long. Since you have a year to probe her for information, I suggest doing some research to see if you can ascertain where the ancestors came from. Other relatives on her side of the family should be able to assist, or research her parents to see where they originated. With more information it might to possible to at least get her to an area where her family came from rather than a generic visit. You can check the national archives for census records to find when the ancestors first showed up in the U.S. and work backwards from there, possibly finding the ship her ancestors arrived on and which port they departed from. Those passenger manifests sometimes give passenger home towns or counties. If she has any mobility issues keep in mind that a number of tube stations in London have a lot of steps without escalator or elevator. I like all three countries equally, so you'd make a good choice no matter which you chose.

You can have a wonderful trip in any of these three. If she has no strong preference, then it might be time to look at some of the secondary features of planning this trip. Is there one location where airfare is quite a bit less expensive than another? You are buying 8 tickets after all.....

What type of transportation do you plan on using? Will you use public transport? Rent two cars or a huge van? Which place has the best options for what you will need logistically? Is there one location that will match your budget and lodging preferences better than another?

It might be best to give her a card this year, with a note about the plan for next summer, to make sure she's part of the planning process. That's a BIG thing to decide for someone else's travel plan without their input. To make it more of a surprise or a present this year, perhaps wrap up a travel DVD for the areas you're considering. As well-intentioned as a total surprise can be, that's a LOT of things to decide for someone else, especially when she was not highly specific. The planning time could be very fun, and at 75 years old, she might have some specific places she wants to see but never really told anyone. A group of 8 people probably would really benefit from discussions and communication about the trip plans.
To answer your question, I would probably plan time in Dublin and mostly London, but that's just me, that might not be what your MIL has in mind :)
I hope you all have a great time!

I agree with Alison's advice. A transatlantic trip of 7-10 days could be an expensive disaster if the 75-yr-old is not in on it during the planning stages.

I disagree with those who think 7-10 days is long enough to travel around more than one country. Given your 8-person group and range of ages, wrangling all of your belongings and adjusting to different surroundings is going to eat up a lot of time and energy. My advice would be to choose one country, with input from your mother-in-law.

Odds of nice weather are better if you stay toward the south.

With that big of a group and 7-10 days, I would stick to one country. With teenagers in tow, I would be tempted to pick somewhere with a city that they can have some of their own time and easily meet up later in the day. Also somewhere where day trips would be possible. Based on this, I would most likely go with England and make London my base.

Nice of you wishing to surprise her but you will have 8 on the trip all different ages. You need to keep them in mind regarding things to see and do as well.

For this brief sojourn I would make London your base.
With Street markets, iconic sites, free museums, 1/2 price theatre tickets, gorgeous royal parks and all sorts of restaurants, cafes and pubs all 8 individuals will enjoy themselves.

Keep in mind that summer months are the height of tourist season. There will be hordes of people. Lines will be long.

Is there anyway you might consider traveling in late November giving up the traditional Thanksgiving and spending it in London? If you plan it right and book airfare early enough you’ll get great prices.

Although there will still be tourists and the kids will miss a few days of school you won’t find masses of people at the iconic sites. Yes days will be shorter with sun starting to set around 4pm but you’ll also find Christmas lights, the free Winter Wonderland in Hyde Park, pantos ( traditional pantomimes) and cheaper accommodation costs. Temps will vary but usually early 40’s, a scattering of rain but mostly grey or blue skies. Bring gloves, a lightweight rain coat and sturdy shoes. You’ll be good to go.

As an example of fewer people, a friend who had never been to London joined me last year, flew in on Thanksgiving day from California. Westminster Abbey on her list of must dos. Went 3 days after her arrival. I’ve been there a half dozen times over the years. Last November’s visit was the best. Honestly we arrived when it opened, no line, used our 2 for 1 voucher and went inside. Spent 2 hours meandering cuz we could. No claustrophobic hordes. No massive tourist groups bumping into one another. It was great.

Chat with you’re Mother in law. See if you can get a better handle on what truly interests her.

Create a budget. London isn’t cheap but it is such a great city with so much history I think all 8 of you would enjoy your time there and with planning you can cut costs.

Public transport in London is stellar. Get Oyster cards and use the busses and with a bit of research you can discover which of the tube stations have escalators and elevators so you can avoid stairs.

IMHO stairs are why 92 year old Queen Elizabeth and 97 year Prince Phillip remain in relatively good health.
That and good genes.

If you wanted a day in the country investigate www.walks.com Cotswolds excursion. Or all of you train to Oxford or Windsor.

Best of luck.