[StarlingWings]

As babies, green budgies split to blue will usually have blue around their vent or on their rump, as you can see in the photo of Ky as a baby.

However, violet greens also have a bluish tinge and that is true for the budgie in the first photo and Pyrite in the second (are they both pyrite?). She appears to be a dark green single factor violet budgie, which explains the blush hue on her rump even into adulthood and slightly dimmed green color

However, the extent to which you can see blue on a blue split green bird depends on the individual bird, and additionally it mostly disappears usually after the first moult. Generally speaking, you can't tell if an adult green budgie is split blue or not

 

[StarlingWings]

Ooh, he's a hard one. In the recent photos you just posted he looks as if blue series is a possibility, but i'm confused by his baby photo since there he looks green series, green split blue. Additionally in the "not so great" photo of him in your first post, he looked definitely green series. So I'm honestly not sure at this point 😅

How does the breeder not know for sure who his parents were?