Buying a Multifamily - New Tenant Lease

I have an offer on a duplex that has been accepted by the Seller.  I will be occupying one of the units, and the current tenant will remain in the other unit.  The current tenant is paying roughly market rent and is subject to a month-to-month lease.  I've reviewed the terms of the current month-to-month lease and would prefer something a bit more fulsome.  A few questions about this:

• Does anyone have experience requiring a tenant to sign a new lease after a sale closes?  Any way I can force the Seller to have the tenant sign this before closing, even if the Seller isn't party to the new lease?
• How about requiring the tenant to obtain a renter's insurance policy after closing, even if a prior landlord DID NOT require it?  

My main question is figuring out how to get the Seller on the hook to make sure that the tenant signs the new lease and obtains a renter's policy before or simultaneous with the sale closing.  

FWIW, this property is in Portland, Oregon. 

Thanks in advance for any advice.