Previous tenants are month to month with no lease

[Kyle Wenger]

I have a 2 unit under contract, the current owner told me tonight that the current tenants are month to month, but never signed a lease or gave security deposits. They haven't been late on any payments, but they are employees of his so if they don't pay he deducts it from their paycheck. He's also charging them a little under market rent. He says they wouldn't pass a credit check. When I take over the property on day 1. What must I do? Have them sign my own lease and collect deposit? Or do I give them notice letting them know I won't be renewing their previous deal with the previous owner. Should I worry about a problem of them not leaving since their isn't a previous lease agreement? Help me understand the process that needs to happen.