I have chickens and ducks together. We only had 4 ducks (2 males, 2 females). The problem arose when our male duck would act similar to the rooster in trying to aggressively win dominance in the pecking order. Because he was larger and stronger than our roosters, his dominant behavior bloodied our roosters. That duck actually became dinner. Our remaining male (Muscovey) duck and two females are sweet, and there isn't a problem. However, if they couldn't free range all day, I think there would be problems.
Geese, from my understanding, can be too aggressive to be left with chickens. However, I can't say that that's true. I've had no experience there.
We have chickens, turkey, and peafowl living together, more or less. They are free-range, so they have their space.....but basically the only issues we have run into is that the turkey, when having bad day, will attack a rooster (No tears there) and chase it for a minute or two, and that the peafowl will, upon finding a chicken nest, chase the hen off and eat all the eggs. We have also had issues with a peahen (without chicks) try to chase a mother hen away from her chicks. Otherwise, all is well.....just make sure you give the smaller birds a place to hide away from the larger ones.
I have 30 chickens (hens and roosters) (standards and bantams), 3 turkeys, 7 ducks and 7 geese and they all free range together. I have never had a problem at all. They have been living together for years. I have a mallard and crested duck who work as the yard security guards but they waddle around for fun and try to mount the hens every now and then when they are feeling "frisky". The ducks aslo bust up any rooster fights. They live in perfect harmony. Without seeing it for myself, I too, would be skeptical about having all of the animals together. The only thing I will say is that for feeding purposes, it may be a nightmare if you're feeding different feed if your yard/property is not set up for it. You would have to separate all who are eating different feeds. For example - laying pellets, crushed corn, etc. I enjoy seeing all of them together.
i have a fenced area of about 150X 250 feet...????? someday i will measure it.. 6 foot fence with 2 strands of hotwire,, on the top and outside.. so no dogs, coyotes,bobcats come in...
i have aprox..15 large chickens, 25 banties, 2 wild turkey, 3 guinea, 8 geese, 1 lonly duck.. i have several covered "houses" with nexting boxes and roosts... and i do NOT lock them in at night..
they all get along..
i did have to seperate my 2 TOM turkeys because they were fighting over the ONE girl... but other than that...
My chickens, ducks and turkey play together during the day and are locked up in the same coop at night but the chickens are on one side and the turkey and ducks on the other. The ducks are in a pen. They were all together at one time and I chose to seperate them before there was an issue I would regret. But before I seperated them I never did have a problem. I just did it for my peace of mind.