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You are dealing with living animals. No one can give you any guarantees. Chickens are flock animals and have developed ways to live together peacefully but every now and then you get one that didn’t read the memo and just doesn’t act as they are supposed to. That can be of any breed and any size.
Are you crazy to even think of that kind of mix? Absolutely not. There are some things to consider and some things you can do to help make your odds better for it to work, but many people have mixes like that and it usually works out fine. I’ll probably make some of this stuff sound like you are headed for disaster but that’s not the case.
I assume your Polish and Silkies will be bantam? A Brahma is a huge chicken, Orpington are large also but not as big. All of them are known as gentle breeds but in any chicken flock you have a pecking order and a flock master. It’s not at all unusual for a bantam to outrank a full sized chicken in the pecking order. It’s more about spirit than pure size. You are likely to see some conflict when they are establishing the pecking order and flock dominance, but if they are raised together as chicks they normally work it out without a lot of serious issues. Your space should be Ok if they are raised together as chicks. If you try to integrate older chickens, even of the same breed, that might be a little tight. You can follow the link in my signature to get some of my thoughts on room. While what you are talking about will probably work I find I normally have fewer behavior problems, more flexibility to deal with problems, and I don’t have to work as hard if I provide extra room. I’m all about making my life easier.
Silkies and Polish don’t look like “normal” chickens. They have funny feathers and head coverings. Occasionally chickens may peck their feathers, especially if you integrate as older chickens. This does not happen all that much. It’s not something I’d be overly worried about, but something I’d watch for. You can get the same kinds of issues with chickens of the same breed and color, let alone chickens with differences. It’s just part of keeping living animals.
Silkies can’t fly. If you provide ramps or steps so they can get to roosts they may roost or they may be content to sleep on the floor. They may be a little more prone to sleeping in the nests if they can’t get to the roosts and want to sleep up a bit higher. Consider them special needs chickens that may need some help getting to nests and roosts. Even if they can get to the roosts they may have trouble getting down.
All your other chickens (and maybe the Silkies) will want to roost on the highest thing available. Your roosts need to be noticeably higher than the nests. That can create a few issues for you, some of them contradictory. I don’t know where you live and what your weather is like, summer or winter. Heat is normally much more dangerous to chickens than cold. In hot weather you need good ventilation so the coop can cool off. In hot weather that ventilation should be high and low. In really cold weather you still need some ventilation to exchange bad air for good. Chickens and their poop produce ammonia and extra moisture which need to be vented. But you don’t want a direct cold breeze blowing on them when they roost. Openings over their heads take care of this problem. Any breeze is higher than them so doesn’t bother them. But in a 4’ high coop, you may have some challenges achieving this. Some people are successful doing this but it’s something that you need to plan for.
Brahmas are really heavy birds with wide wingspans. You don’t want your roosts too high. Some people are concerned that they may hurt their legs jumping down from a higher roost. I’m not convinced that’s the entire problem. The higher the roost the more clear space you need for them to spread their wings and fly down without bumping into walls, nests, feeders, waterers, or something else. I don’t have Brahmas but most of my chickens prefer to fly directly down to the ground instead of using intermediate stops. Your Brahmas may use the Silkies’ ramps to get down. Each chicken is an individual. You can never tell what any one will do. But you might need to watch your coop layout to provide for some clear space for the others to fly down.
I don’t know where you plan to get your chicks. My Pet Chicken will, but most hatcheries don’t even try to sex bantams. Even if they do, vent sexing is not always 100% accurate. If you get them as chicks it’s possible you could wind up with one or more roosters. You need a plan for that. If you keep them (they normally have a lot more personality than pullets so you fall in love with them) you probably need more room. This is an issue with any bantam, not just Polish and Silkies. Vent sexing on full sized chickens is not always 100% accurate either. This is not related to your choice of breeds. It’s always an issue with any chicks but especially bantams.
A lot of people combine different breeds like that. Silkies and Polish are both really popular and are often kept with others breeds. You are certainly not guaranteed to fail if you try. Some people have many of these issues even with chickens of the same breed and color. When dealing with living animals you don’t get guarantees one way or the other.
I wish you luck!
