If you hatched the keets out in an incubator... they won't know who their Momma is, and the flock may not accept them... and may just kill them or run them off if you try to integrate them while they are so young and small. So in that case, yes they will need to be housed (in their brooder) where the rest of the flock can see them for at least 6 wks once they are old enough to be off heat and outside (which is usually at 6 wks old), then after the 6 wks of being confined is up you can try integrating them and see how it goes. You may have to separate them tho and try again in a couple more weeks if the adults are overly aggressive towards the new additions. It's not always easy to merge new birds into an existing flock... and the new additions usually go thru quite a "hazing" before they are accepted into the flock (if they ever are), and it's usually made very clear to them where they stand in the pecking order (which is always at the bottom).
If one of your Guinea Hens hatched out the keets tho, I would just keep the Hen and keets (and maybe the Daddy Guinea too if he wants in with them) confined in an area that the rest of the flock can interact with them for several weeks so they can get used to the keets but not get to them, and then let them all out to integrate after a few weeks once the keets aren't so fragile... the Momma Hen will do the integrating for you, but be sure to be ready to step in and separate everybody again if there is too much aggression directed at the keets, and then give it a couple more weeks and try it again. Sometimes the whole flock will act as nannies and help raise and protect the keets, but it depends on the particular flock and coop/pen/free range set up.
