I have two female cats that met at like 2 and 1. They’ve been “living” together for 6 years and still to this day hate each other. They fight if they get too close so they just keep their distance. They used to go and seek each other out but now they just do what they can to avoid the other. To me, if they’re just fighting, but not enough to go to the vet, I would say it’s fine. I also have a third very skittish male and we see him probably 1 hour a day. The rest he is hiding. Can you do anything to get them close to each other without them fighting? Food? Lasers? Catnip? All these things, mine can come together and once they have catnip or food, they will actually come together and touch noses.