Life would be so nice if she would leave and move in with my grandmother or into a 1-bedroom apartment. But that's silly and I know it.
But my husband and I don't think we can afford our own place with the price of rent and all around here and there is no way I'm going to yank my daughter out of this excellent school system when she loves it like she does.
I agree with above - your daughter will be much better off with a happy sane family life and a mediocre school, than a great school and a crappy home life. To me it shouldn't even be a factor for staying. No factor is good enough to allow you to stay.
I was backtracking to see the living arrangement explanation... Can you ask her to live with her mother? Your family can't afford an apt. alone?
There is no way on earth your kids will grow up normal if you keep your family in the same house as her. The effects will be deep and will show up later in life, as we all can attest to that. I hope you can work something out to get away.
I hope you see a counselor individually to work at the guilt you are holding. You don't have to hold on to it.