How do you define and screen applicants over 18 who are dependents?

[Kadia Lawrence]

I have a requirement that anyone 18 and older must fill out a separate application and undergo a background check for a fee.  For now, I am willing to make an exception for dependents.  Do you make an exception or screen 100% of cases? If you do or had to make an exception, how would you objectively and consistently determine a dependent? (E.g., person in college not working, an elderly person or person with disabilities who is cared for by the main applicant, etc.? Not sure if these definitions run into fair housing issue, especially if it's someone who has a disability.  I would not want to ask or validate that.)