That's great that they're getting along so well.
Maybe something in this TCS article will be helpful: Do Cats Get Jealous? (and What To Do About It When They Do)Sarabi gets jealous and voices her displeasure by peeing on the floor by the front door (yes she has had all the proper tests run and she is perfectly healthy. This is a behavioral thing she has done since before she even came to us) So that’s something we are still working on.