It's anyone 's guess what will happen when you mix the flocks. I expect they will get along fine after some initial blood letting. Of Course, I do not believe in well behaved guineas, they are a myth like the Easter bunny or tooth fairy. Spoiled ones I have seen, I even own some of them, but they have no manners, they have never even said thank you for my allowing them to continue to live here.
His guineas are pied. You can see the white feathers on the sides of the one and the chest on the other. I happen to know where he got the eggs from, and know there is a mixture of pearl and pied in the original flock. It even throws the occasional white. I also know the original flock is not well mannered.