Looks like a mix, to some extent. I see mostly Old English Game bantams, but there's one there with a white earlobe and possibly a rose comb? who is certainly not an Old English.
Most of the time, yes. Sometimes, they'll fight over the eggs, or over the chicks after they've hatched, but usually co-parenting works out pretty well. Have you marked the eggs to make sure no new ones were laid after the hens began setting? If the other chickens continue to lay eggs there (and they often do) then you'll have chicks hatching for several days in a row (Staggered Hatch), and the mother hens will leave with the hatched chicks, leaving unhatched chicks to cool and die.
Unlikely. It happens, of course, but chickens in general usually leave brooded chicks alone if there's a good amount of space. Additionally, the mothers are fiercely protective.
