Hi
Nice birds what ever they are. Without knowing their age, you might have a BC bantam mix. The leg feathers are fine. I have some about 2 months old who are not too much bigger. The BC that has NO feathered legs I find seem to grow faster then those who do have the feathered legs.
The coloring is not always a good way to tell IF for sure these are BC's. I have a Roo who is marked just like a BC, but he is 1/2 Black Jersey Giant and 1/2 Buff Orp. Gorgeous big bird, that looks like a BC, but is not. The true test will be what color the eggs will be. IF these are a mix, most likely you will know for sure when they finally lay. Till then, I would hang on to them. EVEN IF you get one true BC laying brown eggs, it is worth the wait. You should know about 7 or 8 months of age. And then be able to enjoy the brown eggs.