I'd be a bit on the iffy side with 4 roasted chickens at once, even though you make a great one
Roasting 4 will have to have some timing adjustments especially if they are close together in the pans.
(eta: But if this is what you're comfortable with making, then by all means do it!)
I know people upthread have mentioned pork, pork roasts, even stuffed pork tenderloin.
If you're looking for easy, I've had great success with the pre-marinaded pork tenderloins, like these:http://www.hormel.com/Brands/AlwaysTender.aspx
Although Hormel isn't the brand that I usually buy (I can't remember! One I like has a lovely garlic/lemon marinade) Plop them in a covered roasting pan (with space between) and bake according to directions. I put some vegetable stock in the bottom of the pan . . . this helps if you want to make a gravy.
Or, if you prefer, make your own marinade (marinade over night). Pork tenderloin is hard to screw up. Do use a meat thermometer.
Fresh garden salad (ingredients can be chopped 1-2 days in advance)
Mashed, baked, or roasted potatoes (mashed, use yellow potatoes
, can be prepared at least 3 days ahead of time and warmed stove-top or microwave before serving. Baked and/or roasted can be cooked in the oven at the same time the tenderloin is cooking. Baked? Use white potatoes, wash them up/pick out the eyes can be 5 done days before, let them sit on your counter and give a final rinse before baking. Roasted? Use red potatoes, wash them, cube them, let them dry then add any spices that you like. Store in a closed container in your fridge.)
A veggie dish -- how do you feel about brussle sprouts? I'm struggling for a good veggie dish that you can prepare in advance.
Dessert? DD#2 made an awesome!!!! crescent roll single serve apple pie dish, served with vanilla ice cream. Let me know if you want the recipe.
Any way, that's my 2cents worth. Isn't it the truth about having a successful party, the hardest part is choosing the menu?