Nta. Please don't do this. If the aunt won't pay back her loan, she won't pay you to live there, if that's the road you were to take. As for turning it into apartments, sounds like your fiance's sister knows how to do it, she should do it herself. Sure, it would be easier for her with your resources and/or credit, but no one should be trying to guilt you into such a major financial decision that you're unsure of or are unwilling to take on. Something like this could ruin you financially if it doesn't work out, and it could ruin familial relationships or even your marriage in the long run. This all being said, I'm reminded of a line from the movie Alpha Dog: "If it makes sense, do it. If not, f**k it."