You may need to consider rehoming one of your cats. Everyone here with multiple cats that fight - this is NOT GOOD.
Some cats will live quite happily with others - others are top cats or alphas.
If you have more than one alpha and neither will back down - one has to go for the peace and well being of all.
I've luckily never had this problem, but I will say my Diablo RIP, was the
He only once acted out - he bit Lexi girl to let her know she was NOT going to mess with HIM when she tried to become alpha cat.
She got the message and frankly lived in terror of him after that. Though he never lifted a paw to her or any other cat in the group ever again. When he was a kitten he was quite nice to his cohort Sheba, but once he grew up, he would sometimes come groom her, only to jump on her and bite her on the neck (showing dominance).
She would howl and fight back, and then he'd leave her alone. Sometimes he'd go so far as to chase her off the bed where she was sleeping with me. It was quite territorial as far as I could tell. Otherwise however he got on fine with her even to sleeping together when I was away.
All the other cats in our life, deferred to Diablo. As I said, we were lucky. Now he is gone, there will be some reordering of the heirarchy.
I would also like to add, cats do not reach "maturity" till 3 yrs of age. As this time approaches, cats become more assertive, as they are no longer kittens or young cats. This is the time that kittens who were formerly peaceful can start becoming terrors to their elders.
You can allow them to work it out, as I did with Lexi and Diablo and Sheba, and maybe get some puncture wounds and serious bites (as we did) OR you can try to break up and re-direct the aggression.
But keep in mind, if you don't succeed, that one of your beloved kitties will wind up miserably stressed out and you may have to rehome someone. Not fair I know, but true.