Demo 5-6 rows of subway tile and cement board in the shower, pull up the fiberglass pan, have a new drain put in.

I doubt selling is not allowed.

Sorry to hear that you are not able to afford a small MF house hack, but I doubt many 19y/os could. 

I doubt it covers his mortgages payments, but helps a significant amount. 

He or she may understand and allow you to break your lease, although doubtful as vacancies cost landlords money. 

You can try to negotiate but I doubt they will move much.

I doubt it.Can I ask a few questions to tailor some advice your way?

The lender will ask where the money came from and, as I mentioned above, if the partner owns more than 20%, the bank will want that person on the mortgage.Without deal specifics I highly doubt HML is an option here.

I’d still call your city 311 or similar to try and get it cleaned up... but I doubt it’ll be an issue.

I see you want your uncle to change, but I doubt he feels he needs to change, there is a big difference.