Well I took a gamble. I have an easter egger hen that adopted 13 chicks about 4 weeks old, they are now 7 weeks old. The other day they were off by themselves and she was back in the coop sitting next to another batch of 4 week old chicks, while her adopted young were playing in the pig pen. I released the new batch of 4 week old chicks, along with their 4 week old cousins (guinea keets). She took to them initially, but later ended up back with the older chicks. We kept an eye on them throughout the day, and no hens or guinea's were picking on them, so we left them out. About a week has gone by, and the 4 (now 5 week) old chicks and keets are staying in the coop,(peeking outside occasionally) not being pestered by anything else. Perhaps it is because the coop is fairly large, or the fact they have plenty of hiding places, or perhaps because the older chickens (adult guinea's are in separate coop) are outside most of the day.
I am presuming that when the keets get to exploring outside, they will hopefully migrate towards the adult guinea's and all will hopefully be well. Crossing my fingers.