Check one or all occupant applicants for a rental?

[James Conaway]

What is the common rental best practice for qualifying multiple occupant applicants that will reside in a single property?

By qualifying I mean, asking for an application, running a background/credit check, verify income, etc....

Do you only check one that qualifies for all the misc requirements? or every adult that is going to reside in unit?

I think I know the answer, but want to verify. You would require qualification for each resident because if one leaves the others have to qualify individually.

What is policy if one has good credit but the other doesn't? For example, if it's a married couple where one has great credit, but the other has terrible credit?