We don't want to commingle funds (we're adults and appreciate keeping parts of our lives separate even though we spend A LOT of time together - more stereotypically mushy than any relationship I've had before) so for us a monthly rent check to one or the other was the ideal situation for our relationship.  

For example, my city allows no more than 3 unrelated adults.

Fair housing laws are federal, and then some states add additional protected classes.You can say that someone who is younger than 18 may not sign a lease with you, because they aren't an adult yet.  

@Max Tanenbaum excellent point about the puppy vs adult and the landlord reference. 

I have a 5 bedroom house that I am currently renting to 4 adults and 2 children. 

I suppose for any situation with more than one adult tenant, it would be a good clause to include.

Listing all adult occupants on the lease as jointly and severally liable is the right thing to do.

So, maybe two adults and one kid, vs two adults and at least two kids.And families with extended family living with them, are unlikely to be looking for a two bedroom, one bath home.So, my vote is to leave it alone.  

There is no inventory around Seattle but I will buy in the South and South East states.3) I agree that you can't change adults for the most part.

Maybe, adult diapers, Depends The turn key companies are in business to make money, and the longer they have been in business the more money they have made.