Are any of those groups going to be overlapping? So would it matter if you served the same thing at 2 events?
And any dietary issues to watch? Veggie, gluten free, dairy free etc?
I think a lasagna would be a good buffet idea for at least 1 event. Sides of green salad, coleslaw, garlic bread, olives, tomatoes. Lasagne can be made in advance and frozen, to just bake on the day. You could do a separate veggie version if needed.
Slow cooker, could be great to do slow cooked stew/casserole etc, or to just reheat dishes you've made in advance. So stew, beef bourgigne, curries etc could all work well. Stewing meat tends to be cheaper, and tastes delish if done slow and tender, and even better if done in advance and flavours have a chance to "meld" together.
Stew, with mashed potato, side of peas if you need more veg than what's in the stew, and maybe a green salad and French stick could work well.
Chicken and mushrooms in a creamy, white wine (and tarragon is a great herb for this) sauce can be served with mash, rice or pasta - depending on tastes and eats well as a "fork supper" dish. Chicken thighs are better than breast for sauce type meals, and cheaper too. Again, green salad, French stick, maybe coleslaw or potato salad as sides. Also another one that can be frozen to reheat.
Beef bouginonge (sp?) I've already mentioned - serve with mash and maybe some steamed/boiled carrots on the side, French stick, green salad.
Buying part-baked French sticks or batons, and cooking them in the smaller oven to serve fresh and crusty, could work great and save on last minute shopping daily!
Some kind of pork and apples and beans type of stew with mash or rice?
For deserts, I would probably try and think about traybake ideas for a few - brownies with ice cream, bread and butter pudding, stick toffee pudding, etc. And maybe a cheesecake that you can slice for 1, but any leftovers can be served already sliced for the next event?
A big bowl of fruit salad will also be a useful thing to have in the fridge, and that can come out again at a second event.
Is it worth thinking about a cheeseboard?
Or large boxes of chocs that you decant into small bowls on the table for with coffee etc? Or mince pies?