@jhutson has a great answer.
Here’s my additional two cents.
“Title” is a nebulous concept of property law which is state-specific. Who the “state” declares the owner to be (through database, or Title Certificate, or whatever other state-specific means of identifying the home) may not be who the county or other taxing jurisdiction thinks is the owner, which may not be the actual owner according to bills of sale documenting the chain of title down to you.
All of these items count for something, and “behaving” like the owner counts for something too. If the home is abandoned the landowner can usually get title free-and-clear through the state’s abandoned property process. Since you are the potential landowner, only someone with a superior claim could really defeat you, and you cover your bases by not screwing this up.
If you want the homes, act like the owner and get title or flush the owner out with abandonment proceedings (and figure that will cost you something in money, time, and aggro).
If you don’t want the homes, you’ll have to tear them down (get them condemned?) or get someone to haul them out (and bond them for ownership, but that makes it their problem and not yours.).
I would NOT assume that purchasing paper insulates you from any liability with respect to home ownership. The “paper” IOU may be worth less than the paper it is printed on (i.e., a liability not an asset). Treat it with respect and hope it pays off and you can deliver the title because you may be in trouble if you can’t (but liability surely limited to damages of the amount reportedly owed). Right @KurtKelley?