My sister has three male cats. Figaro (neutered) is the oldest, I believe he is 10. Chan (not neutered) is about a year old and Angel is a little under a year old, not neutered and sprays all over the house. Angel is the newest cat in the clan though. My sister got him about 6 months ago.
The best thing to do is to neuter the two younger ones. Unfixed male cats are bound to try to dominate other cats in the household at some point. If they are not met with dominance by another male, they will take over ruling the house by spraying and picking on the more docile cats. By getting them neutered, it usually takes away the hormonal aggression and drive to dominate the others. After neutering, it may take a bit of time for full affect, as the hormones slowly leave the body, things should settle down. Good luck to your sister and her cat problems.
You may want to provide some shelving or perches for the other cats so that they can escape the aggressive/dominant one and feel safe. Feeling safe will make them give off less of a victim vibe which will trigger the aggressive one less
Jackson Galaxy is someone on the telly that has lots of great advice on how to build perches and catios for cats - sometimes it does not take much investment at all
Cats have different personalities. I would separate Angel from tne others. Get cat towers for the others to let them show their dominance.
You could add more climbing and recreational pieces to take down some of the energy. Also you may want to look into getting the other cats neutered.
