subleased duplex with current owner

[Zac Boelkow]

I am closing on a duplex next month. The currently owner splits one side of the duplex with family/friends. He is an out of state investor. He is going to keep staying in the duplex for a while. He has 7 other properties he is selling off so he wants a place to stay while in town. Without his help the "family/friends" can not afford the rent. I am drawing up leases for this property, currently. The current owner will be on a month by month lease. My question is how the lease should be phrased? I have a feeling when he does decide to move out that his "family/friends" will think that they are not on the hook for the entire rent...

Or am I just "overthinking" it?