getting equity out, getting a return

[and...]

Hi
My sister and her husband have a house worth 375,000 with 225,000 equity in it (two mortgages).  They need a minimum of $100,000 to take care of some debts, but can't refinance right now (credit issues).  I would like to help them stay in their house by buying the house (either as the full owner or only as part owner) and then renting it to them.   Any suggestions on possible options for us?  I have credit over 700.  I don't want to take advantage of them, but I'd like to make something from the deal for us, too.  We live in Las Vegas, which has enjoyed great appreciation, though it's slowing down.
Thanks!!