I haven't read through the whole thread, but remember hungry kids are *not* happy kids. You mentioned that the older child is on ADHD meds that take away her appetite & the younger is also very picky & eats very little. It could be that your sister is inelequently trying to tell you what she thinks her kids will eat. How long is the trip? How long have you had the kids for before, sans parents? Mom may just be worried her kids will starve all week.
I have a "picky" eater too, and I know that the first few times we took him to WDW we picked restaraunts based on what was on the kids meal menu. If there wasn't something I was pretty sure that he would eat, we saved it til he he was older. But, fortunately lots of places have chicken nuggets and fries on the kids menu, which is one of his standbys.
For truly picky eaters, they will *not* eat if they are hungry enough, not if the food before them doesn't meet whatever mysterous criteria they have set in their precious little heads. So, plan on having snacks that they readily accept, discuss this with their mom beforehand, whether that's fruit, chips, pretzels, granola bars, or smuckers uncrustables (PB& J) -- mom knows what they will eat "in a pinch." Me, my son loves chocolate milk, so I always bring along packets of Carnation Instant Breakfast, as milk is available everywhere & if he's in a non-eating mood, I know he's still getting some nutrition & won't get the "I'm hungry, but I can't really identify that feeling, so I'll just be cranky & unpleasant" thing going on.
You can probably keep most all of your ADRs, but know if it's a major problem with the food & the kids don't eat, you might be stopping at a CS location to get some chicken nuggets & fries after dinner.
Good luck.
