He is a Sicilian buttercup. They are slightly larger than Leghorns, so not big. He is not thriving if he is only a half pound at that age, but I don't think he is a bantam. With TLC he might improve or might not.
The bottom picture shows Belgian bantams in a few different colors. Also known as D'Anvers.
The top picture might show Swedish Flower Hens. They can be crested.
If the red one is from a hatchery or feed store then it must be a red sex link pullet, despite the massive comb and wattles at such an early age. However, if it is from a backyard flock then it could well be a cockerel.
The comb looks pretty big for 11 weeks. I think it is a cockerel. If it is, male specific feathering should start coming in withing a few weeks, and that will confirm gender.
Yes. I'm not sure which edition that one is. I found an older one at Goodwill for around 10 bucks not long ago, and I have a version from the 80s as well that I used when I used to show chickens.
This book contains the standards used by judges at poultry shows in the U.S.
It takes time to notice these things. Do you have the Standard of Perfection book of poultry breeds? It's a great resource. It's how I learned most of this stuff.
They might be buff Orpington mixes, but not purebred Orps since they have yellow legs, not white.
I suspect they are instead buff Plymouth rocks.
I think they are all pullets. No obvious cockerels at this point.