In 2022, my wife and I helped her sister and husband purchase a home because they could not get a mortgage due to their bad credit.  My wife and I are legally the joint owners.  All payments are withdrawn from our joint account but are paid back monthly by my sister-inlaw.  Does this classify as rental income? Or is this a cost-sharing agreement?  What forms do I need to fill out?  This is a short-term arrangement and they will be assuming legal ownership in the next 2 years.  

Thanks