Oh honey - whata tough situation and hard to have the make the decision so quickly... I cant say what to do or what i would do as i guess it depends on the situation at the time. I'm sure she willbe ok at the ILs place as she stayed there happily last time - and will you and DH be able to relax and have a nice holiday or will you fret the whole time? if you will still enjoy yourselves i guess on balance go - it wont matter in the long run.
I think it is good you are going to the ENT - this happened with a friend whose son was having lots of infections - they gave hm grommets and his speech took off a few months later... good to get it checked out in any case...
Big hugs sweetie - what an awful situation. I am sure you will do what's best for you all. xxx