Mine are a bit like this. We had both Layla and Oscar together when they were quite young so they have basically grown up together. They were quite close and used to sleep together when they were younger but as they've got older and Oscar became a boisterous boy who wants to play fight, Layla has become more and more annoyed with him! She hisses at him whenever he comes near even if he's being nice- she's just not interested. Now we have the little one they are both a lot happier as Oscar and Rufus enjoy being rough with each other and seem to be leaving Layla alone as they have it which is just the way she likes it! She tolerates them but would reall rather be on her own or with people.
I wouldn't worry too much about the fighting, it is usually a case that it looks worse than it is. I would personally only worry if you get any injuries because they will usually be just rough playing or trying to sort out the pecking order in the house. Just try to play with them lots so they don't feel the need to do it to each other as much.
Hope they get sorted!
[attachment deleted by admin]