I would try to formalize your needs and expectations BEFORE the birth, b/c believe me, you aren't going to have energy afterwards for much of anything, esp asserting yourself to people who want to be helpful but just... aren't.
Is there someone you could put in charge of organizing helpers? You could ask for that in lieu of a baby shower or as part of a gift. That person could organize helpers to bring you dinners (so that days don't overlap), as well as chores & people to help with those, and the times that you are okay to have people stop by. It would be a huge help to have one point person organizing things for you... or you could always do it yourself before the birth - give each person a day to bring lunch or dinner and ask them to call first to see if you need anything picked up from the store. Once they arrive at your home and see the white board, I'm sure they'd pitch in if you ask.
Another idea is to post a sign on your door. I recall one mama here had a midwife or doula that posted a sign to the effect of "This family is adjusting to life with twins, which is hard work. Mama and babies are tired, so please limit your visit to 15 minutes. While you are here, please do one chore to help the family, such as dishes, laundry, or sweeping."
Don't be afraid to ask for what you need!