People always come to me and say theywant to adopt siblings so they will love each other more. I tell them cats are not like that. They can be from five litters and all love each other, be from the same litter and not want much to do with each other. Fixing them is key. Get a bottle of water and squirt them if they get into it and yes they are setting up who is going to be the dominant one. They most likely are making noise and slapping at each other vs kicking each others rear right? Keep their nails short so if they do go for it no one gets a serious injury. And for the most part soon one will be the leader of the pack and its all done. That one will get food first, use the litter box first and pick the best spot on the couch or your bed. You cant change that they will work it out on their own. Hard to watch however.