AITA for telling my gf's little sister that she doesn't own our house?

I feel that I must post kind of an edit/update on this since I ran put of characters while typing the full story so I had to cut a little bit that may explain some more of my situation and why we chose to even go this far. So Jeff and Lizzie prior to the move have, for the most part, been completely awesome with everything. Jeff is particularly awesome and is only TA whenever Lizzie has a strong opinion since she wears the pants. However, the reason my gf and I even let it get this far is because we would be extremely stressed paying for the house ourselves. We would basically be living paycheck to paycheck if they didn't have interest in moving in with us in the first place. They do pay a good amount in rent for the basement as well being 450 each. So we think they may deserve to live in a place they like to live in. Its just that Lizzie's demands just keep getting out of control. Jeff has also had issues with how she wanted the bathroom laid out (which would have been impossible with how the dimensions of the room are as well as piping/electrical). We all sat down for a talk recently to talk it through and Lizzie and Jeff know that their demands are ridiculous at times and that their own work stress and Jeff's family working on the downstairs has also been stressful and planting ideas in them about the house. My gf and I told them that its going to stop now or we will find someone else to rent or my gf and I will kick them out and pay the house off until we could sell it for much higher or until we find a replacement tenant. Thanks reddit.

/r/AmItheAsshole Thread