Okay, yes he could also join. I would have him place in his introduction that the two of you are cousins.
I have someone who is helping to clean up some abusers that have joined. He is pretty rigid and I would hate to see anyone get muted. Multiple accounts are okay, but not when they try to get votes from the same person.
Everyone needs to police themselves. I try and be liberal with my up-votes, but when I had a lot of abusers it was taking away from everyone else.