I refuse to stay with my own family in the same room/condo, let alone my husband's family. We took our kids on a cruise for their big Christmas gift this last year and my husband offered his mom a trip on us. WHAT?! I do the budget and an extra person wasn't included. Anyways...he wanted her to bunk in the same room as our kids. YEA RIGHT! We did get two balcony rooms for the 5 of us, with a connecting door. The connecting door was always open, but we all had our own beds. and space.
His mom ended up not coming...which is good. We did far too much walking for her and it would have been the same kind of situation.
My parents understand that we do a lot more than they would want to, but at a place like Disney, my mom does more than we do! She can never have enough Disney! I am trying to talk my family into coming with us in December (the Christmas trip this year), and already told anyone who comes that we'll see them sometimes, but we don't expect them to do the kid rides like my kids will want to do - or even go on the same big rides at the same time....people will be there to vacation. We'll do things together, but also alone.
I'd be honest with my MIL and tell her we appreciate the offer, but is she sure she wants to keep up with the kids in the park. If not, is she going to mind us doing our own thing with the kids.
And if you are glued to their hips, then you go knowing you won't get to do everything. You don't HAVE to do it all just because it's the first time.