Hard to know for sure what his mom was. Thats because white silkies could be recessive white and could be hiding other colors underneath the white, including partridge. Most recessive white silkies hide partridge underneath. These plumage colors may show up in the offspring.
I agree that all are lavender orphington children. The reason why they are white is an entirely different gene, apart from feathered legs and shank color. Its because of the dominant white gene, which leghorns do have. That is the reason why the chicks are almost entirely white, but showing some...