They had pet tenants who were basically charity cases. 

Rent has come from different local charities in the mail this month and she gave me her 30 day notice.

If you say you haven't had a landlord, then sorry.Also, remember you are running a business, not a charity.

Give me $1 and I’ll tell you everything I know, and donate the $1 to charity.  

And then, if they don't meet your criteria, you deny them.Remember, you aren't running a charity. 

How do we support those at the margins while ensuring we are not providing charity that is Toxic???

Paying on time and not being a headache is a tenant's contractual obligation, not a bonus/luxury for me.I like to think of myself as a reasonable person, but the benevolence only goes so far until it turns into charity.

There is no reason to complicate your business by having to rent to a higher risk tenant than necessary.Foster families can be very unstable and will often have "special children" that may cause extensive damage to the property.Unless you are interested in dedicating your business to taking in charity cases just keep looking for regular tenants with less complicated life situations.

I recently learned this when researching for a local charity regarding whether or not they would need to install handicap access to a second floor with only an outside staircase.  

It's charity not business.