IC housing code question: Can 4 people rent a 3 bedroom townhouse?

I just talked to a landlord and mentioned that me and 3 other people wanted to rent a 3 bedroom house he had listed. He told me that the maximum occupancy for unrelated people was 3, per Iowa City housing policies.

After some cursory research, we started wondering what exactly the definition of "unrelated" was. The renters would be me and my long-term SO, and then 2 of our friends. We saw domestic partnerships mentioned, does that count as related? Not sure if I want to get officially married for a rental...

Thanks so much for anyone that can offer help!