They have their reasons even if we don't understand why. Guineas are bullies by nature
and they will attack each other too, to the point of killing one of their own..
This can get really ugly when the current dominant guinea male gets dethroned. I watched the whole flock attacking the once...
If so, guineas are not for you. It is standard guinea behavior.
Giving a problematic guinea male a time out can significantly change his behavior and the flock's behavior.
Guineas can be vicious to each other. Attacks from behind with feather pulling and feather breaking are normal.
The wound you describe sounds more like a wound from a predator.
You cannot sex guineas by their wattles. I have seen cocks with what a person would think were hen wattles and hens...