They prob don't have a pot to piss in and can't afford coming after you for anything.

And because you are on a fixed income (social security, or any government help) the additional money can go for buying some pot or even something better.Your dead beat friends start doing it and soon the whole community stops working and starts playing this game.

However, this is a problem tenant and I don't want to stir the pot with him. 

Once the first, last, and security is paid and the tenant voluntarily offers more money, there is no issue.

They went to clean the place after eviction and found he was growing pot in there.

You'd be wondering, well then who is going to end up using it, and will they be traipsing through my yard or peeking into my windows, and will my child be safe...or do they grow pot in there...Really, just make it easy on yourself and include it in the rent. 

Notice I didn't say "stay in a bad hand"...because that's the fastest way of NOT staying in the game.Holding onto a house with negative cash flow, is like adding to a pot just because you've already put a lot of your chips in this pot, and you don't want to lose them...like you have a chance with a bad hand.  

Previously, we had to deal with the son smoking pot in the common area, but that seems to have stopped upon our request.  

So, getting him to voluntarily sign a mutual lease termination letter that you all three sign, would be best.Eviction would be a last resort, because she'd have to be named on it, and any eviction action that gets filed, would put her name on an eviction report database, and that would be awful for any future renting for her.If he won't sign with her still living there, the only other thing I can think of is to have her move out and break the lease. 

That way they voluntarily pay you more money, in an amount of their own choosing - assuming it would be acceptable to you.