Buying from a family member that wants to remain living in house rent free?

[Joe Kato]

Well I chatted with a family member that says the mortgage is too expensive to keep paying and they want to sell their 2 family. They rent out half of if and want to remain in the other half, although they would no longer have to make any rent/mortgage payments. They have a mortgage on it for half of market value, and would sell me the house for the payoff amount, then I have a house that I have to rent back to the seller for as long as they want (10-20 years) for free. The other half of the house brings in monthly rent, but a new mortgage with PITI would be $500 more that the one rent stream. Rent could stand to go up ~$200 if confronting the long term tenant, but how do I justify paying $300-500/mo for a house I cannot fully utilize for 10+ years? Is this worth it from REI perspective? Is it worth 10 years of maintenance/repairs to have the home equity that is expected by then?