Overcrowding, especially of mixed flocks when young can lead to aggression from Guineas at an early age, but so can a surge in hormones as the keets start to mature... lots of free range time and extra coop space can help alleviate the issue, but I would establish a routine of cooping them up each night (in either your existing coop, maybe in a separate section, or in their own coop entirely) or predators will start picking them off one by one, and then go to work on getting to your chickens and Peafowl after the Guinea supply has been depleted.
I don't start letting my keets out until they are 12 wks old, mainly because they are more agile by then, a bigger size and they also seem to have a little more grey matter upstairs when it comes to escaping predators and being more self reliant... but that's a personal choice on my part, due to the predator load in my area. If you feel they are safe on your property being let out at a younger age then give it a try... if they start disappearing then obviously you will want to work another situation out until they are older... or maybe even re-home them if you are not happy with how they interact with your other types of poultry.