At three months I would surely think you could voice sex them when you get there. Pick them up and squeeze them like a squeaky toy and see what happens 

No. . don't squeeze them.  .but I'll bet when you pick one up and walk a way from its buddies it will talk for you. I was trying to read about the blue Bibbd and I read something about the drake having some green shine to its head. .but being young juvenile I don't know if that still applies. . best bet is hang out with them for a while and listen to their voice.
On another note. . I didn't realise the blue Bibbed were supposed to be that dark in color. Here is mine. . 
View attachment 1400752 I assume she is just not standard. . probably mixed with other colors. But the baby from her egg is feathering out very dark. . that explains it! I wondered why it was feathering out so dark. I'll have to take a pic tomorrow to show you all.