blimey – I read the OP’s description and thought it would be easy, but from the discussion it’s clearly not.
Seems to be all down to where you consider the losses should be covered
– by the initial investment?
– by the payments being made on the mortgage?… and then on top of it how to you cover the idea of “rent” for one sister living in the house, and one not.
I have to admit, I’m struggling with how to deal with it, and with the OP the best of luck that it goes smoothly for the sisters and he gets lives a happy stress free life.