I've kept geese in the past, usually a gaggle of six to eight adults, augmented some years when I let them raise a batch of babies. You could probably get away with keeping your own goslings with the chickens for a few more weeks, but they really need their own space. The main problem with trying to keep geese with chickens is that, unlike land fowl, geese don't sleep through the night. They alternate periods of wakefulness and activity with napping, which, as you can imagine, would be very disturbing to the poor chickens. Geese also need a deeper water supply than do chickens, enough to submerge their beaks entirely, which can make for a wet mess. And as they age, your geese will become increasingly territorial and aggressive towards intruders of all sorts, yet another reason to get them their own digs as soon as possible. Their own fenced paddock with their own secure shed to shut them into every night and which you can leave open for them during the day to use as shelter and a nesting area makes geese happy and will keep your other birds safe. Once they have their own turf, geese are usually fine being let out to forage over a larger area alongside other species. My gang worked an acre of common ground along with lots of chickens, guineas, turkeys and ducks, and never bothered anybody. They did chase other birds out of their paddock, though, especially if they had a nest on the go...
