I did reply to the other one when I spotted it, but that thread gets buried a bit.
We currently have nine. We have a large 2 level cage/hutch in the living room, at one point there were seven males in there - Iggy, a big grey and white dumbo rat, is the alpha and Mel's 'heart rat' - he has a lovely bond with her. He currently just has two companions, Sprocket, a hooded black and white who is very curious, and Cas (short for Castiel), who is similar in appearance to Sprocket but fatter and more aggressive.
In the attic we now have two 'retired' males - Sherlock, an albino dumbo and former big fat bully, and recently moved in with him is Dean, a small, shy black and white fancy rat. They both have some mobility issues and have been struggling to feed, drink and groom themselves properly so they're in Mel's studio space now so they can be nursed and not have to fight for their share, Sherlock has got some weight and energy back now but still ends up covered in baby food. He hates being bathed unfortunately which is very funny to watch.
My younger son has two big grey and white dumbo males in his room, Fry and Bender - Fry is very friendly and loves being handled, Bender is more wary and occasionally nips but will usually assent to being stroked if he's getting a treat lol.
My daughter has two dumbo females, Chuck and Olive - they're much smaller than the males, very quick, agile and lively so they're a bit of a handful, the lads tend to just potter about. Olive is grey and white and appears to be in charge, Chuck is hooded brown and cream and is the bolder of the two regarding people. They are the only ones who pee on people, but only if they like you.
