Caveat:I have a very small group, & it was even smaller in the spring, and that will affect your outcome.
When I incubate or purchase keets, the brooder is inside. I move it to a patio door each day, initially to let the keets see out.
What also happens is the outside guineas look in. It's always the males who take an interest and come every day to watch, at first for minutes, but stay longer as the keets become more active. The hens have absolutely zero interest in these keets.
By the time the keets go outside, the males are ready to take over. I could write a book on the hilarity of watching male guineas with their babies. Last yr 2 males who were constantly chasing each other took up coparenting while the hen was broody with her own clutch.
By the time the hen's clutch hatched, the incubated ones had moved into the coop & followed the males everywhere.
The hen didn't accept them as her own and spent a fair amt of time chasing them once she was back in the coop with her clutch. But those incubated keets took up nannying of the hen's keets. She had a large hatch, but none were in want of a wing to crawl under or a bird to sit ontop of. When they came out, they were divided up between the males,the older keets and the hen, just like we do when we take a group of preschoolers to the park.
This year started with 2 males from last year's hatch one of those incubated keets, one of the hen's, and a different hen.
I ordered keets from GF and did everything the same,males staring in the window & taking over once I moved them outside, the hen on the nest.
She was ok with the GF keets while broody. They climbed on her, laid next to her..but once her clutch hatched, that was it,& she has zero tolerance for them.
The males kicked into gear watching over the new clutch. They kind of dropped parenting of the GF keets and keep the two groups separate.
That's the long story, and I know it doesn't always work that way. I do think the key is that 4 wk period of look but not touch.