What is the dominant rooster's behavior like? Is it acceptable? When the dominant rooster is removed from a flock, one of the other roosters will take over that position. His personality can change dramatically when that happens and he no longer has the dominant rooster to keep him in line. He may turn out to have a great personality or he may not. You really don't know. If the dominant rooster meets your behavior requirements, that is a strong vote to keep him. How a rooster will behave when he becomes dominant is real hard to judge until he becomes dominant.
Does he meet your goals for a rooster? One of my goals is to raise chickens for meat, so size is one of my criteria. If you are not raising them for meat, size would not be one of your criteria. Maybe color or pattern is important to you?
If any rooster attacks a human, he needs to go, dominant or not. No questions asked.
When you remove some of the roosters, you will disturb the pecking order. You can expect some rowdy behavior while they sort that out. That will probably involve some fighting, but since it is pecking order stuff, it may be mostly pecking and intimidation. If you remove the dominant rooster, it becomes a flock dominance issue. The remaining roosters (if you keep more than one) will probably fight to determine who is the dominant one. They may very well work out a partnership and work very well together to protect the flock and get along great or they may fight to the death. Sounds like yours were raised together and get along now, so the odds are they will work out a partnership, but you never know. When I've done that before, it has actually been fairly peacefullly done, so disaster or all out war is not inevitable, just possible. When you do decide which roosters to take out, I suggest taking all of them out at once so you only go through this "danger period" once. I'll repeat. I've done this before (take out the dominant one and leave other roosters behind) and it was not all that bad, but there is a risk.