I have four cats that hate each other pls help

So the gist of the story goes like this, Back in 2019 I adopted two female kittens at two months. They’re extremely bonded and have always cleaned each other, cuddled, played, and NEVER fought. One of the cats is slightly more aggressive with humans and territorial. The other one is just a love bug who never even hisses at humans or other cats let alone scratch. Fast forward a couple years, we move and about a year after moving or so we adopted two new kittens, a boy and a girl both spayed. We introduced them after a while of separation and sadly our aggressive female cat never took to the kittens and would frequently hiss or fight but never badly. The kittens aren’t as bonded as our OG cats, they’ll cuddle very rarely and mainly do their own thing.

It was completely livable until like two weeks ago. My brother came home from marines for a while and it seemed to have set my aggressive girl cat off, she was on edge again and very sensitive. After he left a couple days ago, she started picking fights with our “kittens” though they’re now fully grown. It’s ended in howling, blood, and losing fur. Theres no rhyme or reason, she just instigates when she sees them and occasionally the girl “kitten” will start things because she’s just on edge around the older more aggressive female. I’m losing my mind, I’m tired of watching my animals tear each other apart and my boy cat running in fear. He’s much larger and could pummel her but he chooses to back down and just protect his eyes, etc. Her aggression is making my two “kittens” so fearful and scared, I don’t even feel comfortable leaving the house for my plans today as they’ve had five bad fights since 6 am, it’s currently 9 am.

I’m thinking of reintroducing them and maybe seeing about doing something to help my older cats anxiety? Everyone writes her off as a bitch but to me, she’s just anxious and very emotional. Nobody really notices the things I do and how sweet she can be with constant attention and positive words, her behavior genuinely improves but not to the point I need it to and clearly it’s not always consistent as this fighting has begun and somehow been worse than ever before. Any advice on how to make them all get along or any ideas as to what the problem may be? I’m completely out of my league here.