We had the craziest staggered hatch last year with keets of all ages brooded together. I think that the keets did much better at accepting younger members than chickens do. These keets got so used to new additions that they barely blinked when I added a new one, even when they were several weeks older. I did worry about them running over the younger keets, so when I ended up with 6 week old keets, a 2 week old keet, and a newly hatched keet, I divided the brooder to keep the two youngest separate from the much bigger and older keets. The younger keets hates this arrangement and would desperately try to get to the older ones. The older ones were so sweet with them, they would lay right next to the divider and chat with their young broodmates. I had to get those older ones outside and wanted to keep them familiar with each other, so I made a crate with brooder plate in the coop so they could all be together. At this point, keets were 8 weeks, 4 weeks and 2 weeks. Well, the two younger keets managed to get out of the crate, so when I checked on them, they were all together. They seemed so content snuggling together that I didn’t have the heart to separate them again. The older keets fought with each other, but they never attacked their little junior flockmates until they grew up.Went looking for sav-a-chick, nutridrench, or a similar thing, but everywhere I went had an empty spot on the shelf...
Got home and a couple of the bigger keets had made it over the brick divider. I'm assuming they climbed over each other, since one got left behind. But no one was picking on the little guys, and the littles are better coordinated now so I just have them all together. The size disparity is noticeable, but it doesn't seem so bad now that they're not completely helpless.
Guineas just like to be together, I guess. I have adults and just recently put month old keets (hatched from our own stock) in a coop by themselves. The adults are curious and will perch on the roof or other nearby structures. Until they forget what they were doing and go do other dumb Guinea things.