This is happening because you raised the keets with the chicks. The imprinting removed the guineas ability to understand that chickens are not guineas.
If you want guineas and chickens to get along, brood the keets by themselves and house them separately from the chickens.
It is pretty normal for guineas brooded, raised and cooped with chickens to eventually become terrorists to chickens .
It usually starts with the guineas' first breeding season. The guineas can and do attack en masse.
I brood, raise and house my guineas separately from my other poultry. The...