I have experience with adult kids living with parents, but from the other side. My husband's daughter and her husband, 6 y/o and infant were living in our home for almost a year - and it was NOT FUN! We agreed to let them live here while they were looking for a house with just a loose understanding that they would "help out with groceries, housekeeping & utilities."
They never gave us money, and my husband didn't feel comfortable asking his daughter. His reasoning was 'well, they must not have it to spare.' Of course I didn't feel it was my place b/c she was my step-daughter, though she and I were both adults when I married her dad. We had more of a cordial friendship which was great.
It put a huge strain on all parties involved, including her 2 kids and my husband & my 2 kids. They ended up moving out without any major fighting, but the resentment is still there.
All i'm trying to say is this: If you decide to do this, have an honest discussion BEFORE moving. I think it can work as long as everyone is on the same page and there is open and honest communication.