It seems the house manager guy stuck his foot in it when he let you know about the other people going back to the other house.
That's not your problem unless by helping him not to get in potential trouble actually helps you in the long run. ? Mmmm..
I'm the type that sits on a problem or discussion with another till the time is right. Sometimes that might take
weeks (teenage daughter... moods :-D) and sometimes I just let it go because the fallout isn't worth it or I found a better way to approach.
Annnnnd- as much as I don't like to give advice, I'm gonna on something else - this guy who constantly is talking about God and/or citing religion should really be spoken to directly about that by his supervisor.
As much as a God fearing woman that I am, I don't use my beliefs as fodder for arguments or directives.
It's a really bad way to communicate with others and is often isolating and causes division oftentimes. A person can learn how to not bring religion into conversations but it takes someone to let them know that they suck at talking. My brother is someone who does that and I have no problem saying "God has nothing to do with this discussion. Can you just address this?" He often can't but I at least say something which helps me to not spontaneously combust by holding stuff in.
I hope you manage to get out of that house soon. It sounds like a pretty toxic environment and I also don't think it's your responsibility to be taking on a dementia roommate. Would seem you have enough on your plate without the added stress of that.