Edited to add: I have Ancona ducks from Holderread. The markings are not standardized on Ancona as they are on Magpie. The reason I say they may be crosses is the foot and leg color....the Magpie does not have dark feet and legs. In today's breeding, the ducklings can be heavily marked like the Ancona but are supposed to be light. But the black head caps say Magpie. Ancona are marked individually...no two alike.
Well if I had to guess right now, I would say a Magpie x Ancona but as they start too feather you could get a better idea of their cross. As ducklings they look like magpies with dark feet and legs.
Could be some kind of silver appleyard cross...they have dark mohawks...I don't know. The black feet?
I would guess maybe a cayuga crossed with something like a pekin?