(this is called reserves) On a 300k price 15% is 45,000 but you would need closing costs and the required reserves for your particular situation as mentioned above. 

This classic “leveraged buyout” is the basis for what we call “private equity” (KKR) today, but of course requires significant capital, business and financial expertise and experience, and a business target large enough to attract top tier management with incentives to out perform the previous management.   

This area is really in need of affordable housing, but with the large down payment requirement it rules out this option for many.

Note if they move you will want to be sure to send them an accounting of their security deposit within the required time.

She refuses to do so, bc he has legal issues and want qualify and meet the lease requirements.

They are inexperienced and do not know what requires a permit2.

It's easy to obtain, costs very little, and doesn't require extra, on-going effort to maintain. 

Do you know trustworthy contractors that could complete the required work?

You also may be required to have certain drainage features built into the land, building setbacks from the curb, number of parking spaces, number of handi-cap parking spaces, space for trash, et cetera.

It might be cracking and heaving inward which might require both dealing with exterior ground moisture and also stabilizing the foundation from the inside with one of a few options.