You can be of an expertise and maturity level that far exceeds your appearance or legal age. 

I know I cannot get him out, sheriff has to do it, but he has no legal rights, and I don’t want to pay his utilities.

@Adrian Vega A DBA will not help you for tax purposes, for legal purposes, or for liability protection.

@Robert LindsleyThere are many properties that are legal non-conforming.  

It's also important to keep in mind that every additional rental property you own is another potential source for legal trouble, so if you grow to a certain size(and Terrell might be approaching that size), it's almost inevitable that some tenant will get a valid reason(such as falling through a porch you didn't know was rotten) to sue you over a 10 year period.

@Jay Hinrichs @Steve Vaughan Looks like there's a lot of reasonable and good thinking here, but I think it's easy to oversimplify protecting yourself legally, especially if you start small and grow.

If an occupant is not following the rules but the tenant is, are their legal actions I can take to evict an occupant that isn't on the lease?

It is not impossible I am sure, but those house-hacks where you get paid  to live in MFR seem to be rare here. 

I really want to invest in positive cash flow properties but it's impossible in New York.

Are there any legalities, rules, or procedures for renting out unofficial units, such as an attic unit?