My goal is to hold this property and use my lengthy experience as a short term vacation rental owner to rent it out, which I am already doing. 

Rather than go in length, I figure I'd give you a link to a pretty comprehensive break down of the design process.

Evict your tenants (in Philadelphia this is a lengthy process) or try to buy them out. 

Let me pre-apologize for the lengthy post. 

I don't want to make a mistake, and lose my summer's rental income because of a winter tenant forcing me into a lengthy eviction process, or because of a short term summer tenant refusing to vacate the property for the next tenant.  

I have a lengthy Legal Opinion, from my seasoned Legal Team regarding this matter.

It'd be too lengthy to type out in this chat forum, so we can always email back and forth. 

If done legally and at arms length is probably the best strategy since if there is limited equity to seize, then it is quite possible the claimant with find it hard to get an attorney to take the case.

If you're looking at a situation where the seller has just been talking to their lender and is not fully pre-approved, then it is lengthy.  

You will have major expenses, like roofs, sewer lines, boilers, a nasty eviction, a lengthy vacancy, a lawsuit, and any of a number of other things.