[Theory] Brother and sister? the legendary theory.

While lugia and yveltal look so similar and are joked about as being brothers, could this be true? I think that not only are they brothers but they have a sister. Their sister is none other than.............Lunala? Are these guys all related? They look so similar but could they actually be related? all three were in the games that seemed to be second to the other one. Moon seems to be second to Sun, Soulsilver to Heartgold, and sometimes Y to X. thoughts? Can someone prove this to be real? Will anyone ever know?

I would need more evidence other than just looks. There is no evident links in the game so I'd put this theory off.

the point of the theory is actually to kind of attract anyone else who thought this and maybe knows something. Nice avatar btw. Sinnoh?