Buying a duplex with tenant and + meth test??

[Monte Blunk]

We are in the process of buying a duplex in an area that is in an area that is "up and coming".   Unfortunately we have some big costs associated with getting the place up to code and safe for tenants on one of the sides (30-50K).  One side is vacant and is very clean and almost ready for a renter.  The other side has a section 8 tenant and this side had a + meth test (level around 2-3). 

We have asked the current owner to give the tenant in the occupied unit 30 day notice once we clear the financing since she is on a month to month lease.  We will then close 4 days later.   We are a little concerned about running into problems with this tenant as it looks like the person on the lease is not actually the person in the unit as well as the + drug use that may or may not be going on in the unit.  There also seems to be an additional man in the unit that is not on the lease.  

Has anyone had similar situations and how did you handle it?  Any things that we should watch out for?   Would love any advice other investors have had with + meth tests and removing tenants.

Also, any ideas on how we make sure we get the rent for the remaining month since she really has no obligation to pay us (but does to the current owner) since we did not sign a lease with her?