Unfortunately the vast majority of landlords do not screen very well and rarely understand human nature.

My husband & I are in the beginning stages of purchasing and converting a SFH in SF to include an accessory dwelling unit. 

I let the numbers (and human nature)  speak for themselves. 

Also as mentioned most folks on this site do focus on dwellings of sorts.

Always do the humane thing!  

All tenants should to be treated equally unfortunately that is not basic human nature.

So I found on the county website this...R-6 These districts exist for the protection of areas that (General Residential District) generally contain older residential structures, some of which were originally large single family dwellings which have been or may be converted to rooming houses or multi-family dwellings, and others which have been built on relatively small lots.

They are also subject to rules governing service termina­tions to multiple dwellings, customer security deposits, payment agencies, back-billing and the refund of overpayments.Municipally owned water suppliers (those of cities, towns, villages, etc.) are not governed by the Public Service Law.

Reach out to a few and find one who will take you under their wing.If you're feeling altruistic, another way to learn and get construction experience is to volunteer for non-profits like Habitat for Humanity.

There isn't even a thought or decision here... had they come to you with a heart tugging humanizing story at least there is a chance you might consider especially if you feel the circumstances extraordinary, or be upfront and honest about whatever hardship they are facing and perhaps you have a solution that works for everyone - but a threat?