So sorry you're going through this. But the situation you're describing is setting you up for PPD...just say no. You have to take care of your health and all your babies' happiness, by not allowing toxic family members into your home, either physically or mentally.
It sounds like you're a great daughter and sister, and far more patient than I would be. But in this situation, being a great mom has to take precedence over the other relationships.
If possible, hire help for the next month or so...and if not possible, what about your friends? Do you have some close women friends, or people at your place of worship, who could help you out?
Beaming mom to DS born 10/20/2010.
The Force is strong with this one.