I'll give it a shot, but I'm not an expert so they may not all be right
Charlie- skyblue opaline spangle
Birdie Baby- yellow face type II sky blue recessive pied spangle
Koko- I agree that he is sky blue dominant pied, but I can't see opaline from the picture since I can't see the back.
Let's see what the experts have to say!
I think that Charlie is opaline violet sky blue. Although his wing markings are lighter than the usual I don't think they are light enough for a greywing and his tail looks quite dark. The shade of blue is not dark enough for a cobalt. Violet sky blues are often mistaken for cobalts
Birdie Baby is a Type 2 yellow face opaline sky blue recessive pied. I breed a lot like this, I think that adding opaline to a recessive pied makes them much more attractive
Koko is opaline dominant pied sky blue like you said
Thank you very much
Zeena for trying to help me, Lindsey for giving extra info why they would be called that way, and Nev for your expertise in budgie mutations.
Nev, you just confirmed something about Charlie's coloring that made me think that he may not be just cobalt, because his color indeed is not something I have seen in cobalts before. But since I don't have enough experience in that field, I could not pinpoint what exactly his base color was.
Even though, his color in my picture may not look as anything special, I often look at him and simply admire him because his color is so different. Now I know why.