Multi-family units are hard to come by.

An investor uncle said he could deed the house to me and include a promissory note that he would be paid by a specific date (4 months). 

Tenants should have no authority to engage contractors without authorisation from the landlord and if they do they should never be compensated by the landlord.

that can be a big determining factor if something like AirBNB will or will not work (or will even be allowed by county/city)What is the layout like? 

By the way, anyone please feel free to jump in and correct me or add to any of these points.The next vague impression I had been given about commercial property is you’ll be dealing with more hard nosed and knowledgeable people.

If it's just speculation, start by reviewing the law to see if there are any unique requirements for a business.

Both properties owned free and clear by our mother but my brother has the power of attorney.

It seems to me that your biggest potential liability at this moment, by far, is not having a lease. 

For example, adding a bathroom can increase your home's value by 10-20%, depending on the quality and type of bathroom.

There is a contract signed by the previous owner for 5 years with 10 automatic extensions, so the contract expires in 2024.