I'm going to go against the grain. If it was me, I would keep the Brahma. I've heard of Wyandotte males turning human aggressive far more often than Brahma males. Brahmas in general are just a more docile breed. And I think your bantam hens will have an easier time escaping from a Brahma than a Wyandotte.
Also, I wouldn't judge the Brahma based on his behavior toward the other cockerel. That is perfectly natural. What counts is his behavior toward you and your hens. You want a boy that is a little afraid of you, and is respectful of the females. A cockerel that shows no fear, even if he is cuddly and sweet now, stands a higher chance of becoming human aggressive in the future because of the lack of fear.
Also, I wouldn't judge the Brahma based on his behavior toward the other cockerel. That is perfectly natural. What counts is his behavior toward you and your hens. You want a boy that is a little afraid of you, and is respectful of the females. A cockerel that shows no fear, even if he is cuddly and sweet now, stands a higher chance of becoming human aggressive in the future because of the lack of fear.