It is. But yours are mixed so it's normal that they have lost this trait. Plus it's highly dependent on conditions as well, so there are cases where they crow around the 4 month mark
Well they definitely look like Oriental gamefowl mixes. They're either going to have a pretty serious fight, or the "common" chicken genes will take over and they could live somewhat peacefully. Only time will tell, if you prefer the stag that's not crowing for breeding separate him with a...
Do you know their breed? They seem like gamefowl to me. If that is the case, unless you separate them it's very unlikely that the dominant stag will let the other one mate