My personal belief, is that a lot has to do with environmental. Dogs, chickens, cats, etc. I breed Basenji's. A lot of them used to be quite nasty and a lot of them still are. However, I believe, that because I socialize the heck out of them, and I am on top of them, and I watch the genetics, I have great puppies. All of my puppies I have placed are good dogs. I have more than one that went to a home with kids and I say the same to each potential owner-socialize, socialize, socialize. BUT, it also helps to have good breeding practices also. I also agree with whomever said the from the discount breeder you basically cannot predict the temperment of the chicks. I would keep trying with them and if they don't improve, I would put them in the freezer.
I am also getting some Standard Brahmas tomorrow. I have been told they are not aggressive, but not friendly either, they seem to accept you are there and that's about it. I am hoping to breed the trio and get better temperment with lots of socialization. However, the gentleman did say that all the hens and Roo they came from are friendly. I really hope second gen is much better.
Let us know how your Brahma grow!!