Thanks for the info.
I was planning on giving them more than required anyway, but now I definitely will. Maybe I'll make them read some of our annoying e-mails to each other as well....LOL. No, on second thought, even I'm not that cruel.
In our case, he owns the house, so he just said 'Yes, move in. Here's how much the monthly expenses are, so if you could give me half of that each month, it would be great.' So there was no formal rent agreement--I just transfer the money to him at the beginning of each month and if he needs me to buy anything for him, he transfers the money to me. When it's my turn to pay for groceries, I just give him my debit card since I'm usually at work. We have access to each others' finances, but they aren't joint. I may just open a joint account and keep a small amount of money in it anyway, just to be on the safe side, and then give them more documentation than they need.
I really appreciate hearing others' experiences in this matter---it definitely makes me feel like we might have a chance.