see a real estate lawyer. without being on the deed, I don't see how you could be owners. the mortgage also presents a problem. if you become owners this might be treated as a sale and many mortgages have a due on sale clause.
an option would be to lend them money, not in excess of the FMV of the property reduced by the present mortgage, and take back a second mortgage. they would still be the owners so they would report the rental activity on their return. you must charge interest and that would be reported as such on your 1040
also realize that while the rental can create positive cash flow, the owners must depreciate the property which can result in a loss for tax purposes. then the owners would likely be subject to the passive activity loss rules.
