This is confusing. Where do you fit in? Are you a R/E agent? It sounds like you are brokering a deal here.
Buy the property from seller Sub2 with seller getting 13K at closing. Then you are free to sell, rent, or L/O to anyone you wish. If you are in MD and property is in foreclosure be careful. Maryland has passed some crazy R/E laws recently
I have a seller with 100,000 mortgage on an appraised 200,000 house $850 payment. I need to get in and structure a no money down deal to his current tennant as a fixer upper deal. You stay and make $XX payment and perchase price of $XXX,XXX. The seller will need about $13,000 to take subject to.