@Donald Cooley
Good questions. You should brush up on the local landlord tenant laws in Michigan (I'm assuming that is where the property is located), as some laws vary by state.
In Virginia, if the tenant has a valid and in force lease, they are protected from any changes. You must honor their lease terms. You can have them enter a new lease at the end of their term, or earlier if they agree.
Another step that I highly recommend that you do is obtain an estoppel from each tenant. This is simply a form that the tenant fills out that states what they pay, do they have a lease, when does it expire, what is the security deposit...basically an abstract of their lease. You want to make sure that what the seller tells you, and provides via current leases, is also what the tenant thinks is the case in regards to their lease.
The seller must transfer all security deposits to you. It isn't their money, it is the tenant's, and you must hold it in escrow (requirements can vary by locality) until it is time to disperse all or some of the deposit.
Those are my initial thoughts, hope it helps. Good luck.