As for lending, personally, there is no way I'd lend for rehab there without seeing a CO and lease.

I am renting a co-op which already has a contract about the rules and regulations for the tenant to sign.

The son could be a co-signer, or not.

It also holds true for an all female household versus a coed household.  

Most LLCs are taxed as a sole proprietorship or partnership, but LLCs can also choose S corporation or C corporation taxation.Without an LLC or other business entity, your personal assets are at risk if your business is sued for something a co-owner or employee does.It is a good idea to start using an LLC when any of the following occurs.You want to buy residential properties with cash and you do not intend to refinance down the road.You want to buy residential properties using cash but not all of it is your cash.

I was thinking of sending her a PDF of the ROP (called a CO in most places) that shows it is coded properly and leave it at that.What do you think? 

I just listened to a podcast by Brick Underground interviewing the CEO of a co-investing company (probably Unison).

So I'd have to do a co-wholesale on a deal like this for it to be legal.

@Adam Harper, if you own a co-op in NYC, and are serious about investing, that is a great starting point. 

The fact that your underwriter/lender didn't recognize your father as a co-borrower should be more than enough to shut it down.