They are totally gorgeous
I think they are all silver greys there
I'd wait till they are 4 weeks then split them in to a tank of males and a tank of females. It's a nice group size as they should all have company and pups tend to do better with siblings to run on a bit at separation from the mum.
They never grow as fast as they are doing now so continue to be very generous with the food just as you are doing now. We feed like this till they go to new homes and I would say they will be ready to go singly at 6 weeks onwards as they look very nice and chunky. Also suggest the new owners feed some growing foods and fresh when they move on.
They usually start bickering about then anyway so watch out for this. Females will fall out sooner than males.
If anyone wants a pup for Christmas I would suggest you insist they take it ether before or after the big day as having on on actual Christmas day can be stressful for the baby.