Quote from @Nick Hulme:
I appreciate the quick replies. A couple follow-up questions:
1. What all needs to be accounted for in the agreement? Sister's rent amount,
term (date of refinance), mortgage payment responsibility, insurance responsibility, utilities responsibility, tenant selection responsibility (since this will be a multifamily property), property management responsibilities including repairs, maintenance...
2. When the property is refinanced a year later, after it has been owner occupied for the required amount of time, will the rate then increase to that of an investment property?
You might want to touch on ownership in that agreement as well, that will be important. With the refinance, unless one of the cosigners of the loan is living at the property as their primary residence at the time of the refinance, it would be considered an investment loan. You don't have to refinance though as long as your sister was ok continuing to be on the loan. Granted, rates are headed down so it would likely be beneficial to refinance in the next 1-2 years.