Sandwiches

If you don't want the hassle, you could buy some ready-made fillings from M&S for some of the sandwiches, or if you wish, get them to make a platter of them for you! I ate some left-overs from a friend's party food from M&S, it was all delicious!

Your could have a retro theme and do fish paste and creamed egg (not together). Nice and safe on the elderly teeth.

Most of the things that spring to mind would indeed go soggy if made too far in advance. Such as egg n cress, tuna n sweet corn or coronation chicken.
Ham or grated cheese are good staples.

When I worked in the nursing home, the sandwich fillings of choice were, egg mayonnaise, cheese, tuna with sweet corn or cucumber, canned salmon. If you wanted something a bit pricier what about smoked salmon and cream cheese.or roast beef thinly sliced?