she also mentioned that she has called the police before when outbursts and abuse has occurred, but it takes 8 hours for them to come, and they have openly told her there is nothing they can do based on their same sex relationship. 

Housing strangers of the opposite sex together is a recipe for disaster.

My system verifies their identity, address history, sex offender registry, criminal background, and a complete credit history.

The tenants might also (gasp) have sex outside of wedlock on your property -- also not your business.

If the two other tenants will be sharing a bathroom, it's going to be hard to find co-eds willing to share with the opposite sex.

Here's what we do:Tenant Net (goodtenants.net) They give us credit report, address verification, sex offender check, judgments check. 

For reference, this is a violation of the Fair Housing Act.You can't discriminate based on sex (among other things)...

I have 3 prospective tenants for my room rental in a SFR under this slow market (vacant for 4.5 mos): A sex offender when he was 17 but he’s 50 now (he told me about it only after I said I had to run a background check).

And there are certain felony convictions that are unlikely to have the state attempting to act on their behalf, such as sex offenders, violent assaults, etc, so you can probably feel free to reject those applicants if you'd like. 

Introduction The Fair Housing Act (or Act) prohibits discrimination in the sale, rental, or financing of dwellings and in other housing-related activities on the basis of race, color, religion, sex, disability, familial status or national origin.1 HUD’s Office of General Counsel issues this guidance concerning how the Fair Housing Act applies to the use of criminal history by providers or operators of housing and real-estate related transactions.