I already did a complete timeline of Kirby time ago; it's not perfect and sometimes I adjust some events to improve it or adapt it to newer games, but anyway.
In my timeline, Kirby's origins aren't explained (simply because there isn't any need to do it), but yeah, I consider GalactaKnignt, MetaKnight and Kirby being of the same species.
In my theory, Galacta is an ancient warrior who fought against an ancient manifestation of Zero, but he failed to defeat him and decided to seal it into the Mirror World, a dimension created by himself with the sacrifice of sealing himself into another dimension forever (the dimensional mirror has angel wings, just like Galacta Knight). Metaknight released him at the end of Superstar Ultra (that part happend before Nova was destroyed, and in particular, before any adventure of Kirby) and then the dimensional mirror appeared, and Amazing Mirror happend. This is why MetaKnight was kidnapped in that game, and it's why Dark Mind resembles soo much Zero.