That can enter US universities from the British, IB and American systems. American or International schools will specialise in US university entry, however.
Selective independent schools will have a US university tutor in the sixth form, and they will make sure students attend college fairs, prepare applications (incl scholarship), negotiate financial aid, and prepare for SATs and other entrance exams. If you go for a British school, make sure they offer this.
At 13 and 11, your DCs should be sufficiently flexible to go with either system.
You shouldn't have a problem in finding a school that is strong in French. It's still the main MFL.
I have taught in ACS Egham and I thought it was a good school - perfect for mobile families. Personally, however, I would put them in a British school if they are here for the long run. An international school is a very artificial environment. You will find that there is a lot of diversity in Surrey, with plenty of overseas students in most schools, especially independent ones.
There are ice hockey teams in Guildford, Bracknell and Aldershot, and most towns with pools will have a competitive swim club.
You have lots of options - where to live, state vs UK independent vs international, co-ed vs single sex, selective vs comprehensive....
You need to pick one and go from there.