K.N.
Oh my goodness T.... I would have LOVED to have another adult present after my baby was born... Another set of hands... And I only had 1 baby to juggle!! You're focusing on the negatives... Think of the positives.
You plan to go back to school AND juggle twins AND your marriage... AND carve out exercise time on top of keeping the laundry under control and the house presentable... AND you're gonna do this (and homework) with how many hours of sleep each night?
OMG, I would be all smiles around her... "Welcome... do you think you'll be able to stay here until the twins are 2? How about until they're 4--can we lock in a contractual agreement on that..?"
Think of her being there as a godsend!!!! (If you're religious, then maybe you can consider this as a divine response to a prayer you didn't know you asked for... because those 18 months after your twins are born will be challenging for you to juggle everything.)
You have a full plate. If you get lemons, make lemonade girl!