Subletting for 1 Roommate

[John Casmon]

So I acquired a new building a few months ago and one of the units is occupied by three roommates (two of them are sisters and one is their friend).

Their existing lease runs through October, but the friend is looking to move in with her boyfriend by July 1 and has already identified someone to sublet the apartment. The potential sublet person is friends with the sisters so they're all on the same page and approve.

My question is how should I handle this process wise? I've told the tenant that the potential replacement has to be approved by me and if so, then we can take the next steps. Should I sign a new lease with all tenants? Do an addendum to the existing lease? And how should I handle the deposit return?

I know I need to walk the unit and execute a move-out with the friend, but not sure how I should process the rest. Any help or guidance would be greatly appreciated.