@Heather1290 What sort of group of 12 people do you envision booking this property? It sounds like you can comfortably accommodate 8 people, if that group includes 2 couples. But 12? I'm drawing a blank. Swinger party? R. Kelly's "family"?
I used to see the double sink in American houses and imagine they were designed for married couples who both had to go to work at the same time and brushed their teeth side-by-side. Well, I've been married for a long time and that concept still sounds gross. Maybe it's a cultural thing, but I think of a home bathroom as a one-person-at-a-time environment, especially considering all the things other than tooth-brushing that it's supposed to facilitate.
When I look back on the two-sink vanity combo (which was hilariously common in the 80s), this is what immediately comes to mind: https://www.youtube.com/watch?v=avb1XbO0EIs&ab_channel=SaturdayNightLive
Maybe it's different in Phoenix though. Never been there. Still, I'd probably be thinking more about that guest-to-bathroom ratio than the sink-to-bathroom ratio if I were you.