I was thinking..."Well, I've never done that"...but then realized dh has! Lol...we took my Mom with us in 2009, and it was the first trip to Disney for
ALL of us. Mom asked if she could travel with us, as she doesn't care to travel alone anymore (driving to the airport etc), and my Dad has zero interest in Disney....
We did have seperate rooms, and that helped...dh, the girls and I splurged on a Pirate room at CB, and Mom had a king room in another set of buildings there (South and North Trinidad...can't remember which was which)..
The thing that worked for us was to "do our own things" each day, then meet up for supper at an ADR...
Even with that, by the end of the week, we were starting to feel the strain...but it wasn't Mom's fault. We simply found we'd made too many ADR's for our own taste. By the time the end of the week rolled around, we were tired of racing to ADRs and having to stop dead whatever we were doing at the required time.
Next time we go (you can see on my ticker) Mom will be going as well if she's up to it (she has terminal cancer, and will be in the last year of her allotted/supposed "time left"), and we'll follow basically the same plan, but have fewer ADRs for supper....maybe do one every other night instead of every night.
I also think we might include her for a Kim Possible mission (b/c she enjoys "puzzle-y" things like that) while dh has a beer or two in Germany (as his patience strains at things like that)...
I still think you need to find some way to warn mil....don't necessarily tell her exactly what it is, but warn her there's a surprise coming from dh, and he really is excited...blah, blah, blah.....
If everything else fails, remember my new favourite saying...
"It's nothing alcohol and a shotgun won't fix."