re: Advice on In-Laws and a Mortgage

I'm trying to summarize my questions/concerns/arguments toward them. Any feedback would be appreciated.

1) What was the reason for buying the house in the first place? It seems to me like it was a place for both <wife> and <sister> to live at the time and perhaps everyone saw buying over renting the more financially viable option? If that's the case then where does <sister> fall into all of this? By no means am I trying to get her into this, it's just a question I have.

2) One thing that makes me uncomfortable is how many unknowns are involved. If we simply had to pay $867/month for the next, say, three months, I can wrap my head around that. It's the fact that it's indefinite at this point that worries me and also the fact that I don't know what is going to happen if it doesn't sell. I get the feeling we will be responsible for half of any losses. If the house value had risen to $300k instead would we also be splitting the profits?

3) If we are splitting everything down the middle why did you get to claim the interest?

4) I feel like we have half of the bill but none of the authority. I didn't realize we would be responsible for this until April (and maybe that's my fault for not asking sooner). If I had known all along I would have tried to get it on the market MUCH sooner. Why didn't we try to do this more like January? I did the yard and the pressure washing and would have been happy to do more had I not been two weeks away from getting married. I feel like we aren't really involved with timing, which real estate agent to use, price points, etc. I know you have spent a lot of time on all of this and making the best decisions but I'm not one to typically just sit back and watch.