We have:
Bantams-
Chocolate Wyandottes
Belgian d'Anvers
Watermaals
Old English Game
Modern Game
Cornish
Speckled Sussex
Silkies
Ko Shamo
Large Fowl-
Lamonas
Appenzeller Spitzhauben
Olive Eggers
Leghorn
Langshan
Barnevelder
Ameraucana
Orpington
You could keep a couple of those yellow legged birds to use to test hatch with your whited legged birds. If any of the offspring have yellow legs, you will know that your white legged parent is carrying the recessive gene for yellow legs.
In my line of bantam SS, the birds with the white breasts at this age are typically cockerels. Looks like you have quite a few of them. I see that you have them banded. Take notes on what you see at various stages and then compare with what you see when they become adults. You can learn a lot...
There is a webinar coming up next week on High Pathogenic Avian Influenza. It's free and being put on by Cornell Cooperative Extension. Here is a link to more information, thru my county FB page.