Interesting. I once kept 28 chicks, mostly pullets, in a 3' x 5' brooder until they were 5 weeks old. Another time I had 21 chicks, mostly cockerels, in that same brooder. All full sized chicks. In both cases they were starting to look crowded but had not started to act up. I don't know how many boys you have versus girls but sex can make a difference in room requirements. In square feet those brooders are pretty equivalent.
Some chicks are just more rambunctious than others. I don't think it's that much breed related. Mine are mostly a barnyard mix and some years the boys are a lot rowdier than others.
The main reason I'm posting is that you had three different boys bleeding. That doesn't sound right. One year I had a two-week-old chick (turned out to be a boy) kill a sibling. They were being raised by a broody, for what that's worth. That chick started pecking at a siblings head until it killed it. Then it started pecking another chick's head. That chick just stood there and let it. Mama did nothing to stop it. That's where I noticed what was going on. It's possible one of your boys is kind of homicidal. If you can you might want to see if it is just one chick doing that.
