Why does roosters croak and other chicken quetions?

so i have a couple chickens and we now have 2 roosters that we thought were females. one croaks, why do roosters do that? and we hold them alot and their not fully adulthood so can we keep the two of them? would they have anger issues even though we hold them? and what about the females could they be mean? and they are bantams mixed with regular sixed so would regular chickens be dominated and hurt them? also dont they have to breed with the same breed or any chicken? and we are getting 2 baby ducklings who will stay with them, will they be fine with the other chickens? (: THANKSSS!!!