I blew up your pic, and just based on your boys comb, I'd say they are maybe 1/4 Silkie? But u shouldn't get a white chick from the pair, but I'm dealing with my own issue of a chick hatching a color that shouldn't be possible from.its parents either but it's here..lol..so I may not be the best...
Can u get a closer pic without the fence blocking the view? If they have crests (puff of feathers on top of their head) they could have silkie or polish in them..what color is their skin, how many toes and any leg feathers?