[souffle]

Sossij is without a doubt a Hybrid. She has red eyes for sure These are not found at all in Winter whites. She is a hybrid with an argente Campbells somewhere in her genetic make up. They can still change colour in winter even if Hybrids. This combo was sold as a Mandarin WW by some but it's still a hybrid. The shape is also wrong for a WW. Once an animal has been hybridized you simply cannot breed out those genes. It is fixed in the the animals and their desendents forever. Chungles is a Sapphire in colour however again though closer to a WW in type and colour he will still be a Hybrid if he came from the same source. He does not have the head type of a WW. I'm sorry but your supplier is incorrect.
There have been pure WW at a number of the Northern Hamster Club shows for sale or collection so I'm not sure where you searched and how far north you are.
I really would suggest you do not breed them. To knowingly breed them and breed more hybrids is unethical to me. The problems that can occur further down the line due to the hybridization can produce pups who may suffer illness and other issues with temperament. One of the main problems is with the mother and the delivery of pups. The two species vary slightly anatomically and if the pups are more WW and the mother more Campbells then the difference in head shape can result in pups getting stuck in the birth canal and her dying due to being unable to deliver them. Both species have health problems such as the eye condition glaucoma, diabetes and neurological problems. Hybrids can 'double up' these genes resulting in pups suffering from these conditions more commonly.
To answer your questions litter size is quite varied between 3 and 15 is possible but average is about 6 I would say.
You need to have cages for all the groups of males and females separately or else within months you will have dozens on inbred pups.
Should you go ahead then you must separate the male as soon as you see that the female is bulgy and looks pregnant. They will mate as soon as a litter is born and I mean literally' as soon as' if not inbetween delivering pups. She will be pregnant again while nusing and a second litter arrives around 22 days later. This is not good for the female to have back to back litters. They will be fine apart. Dad will sometimes take in the male pups as long as you put them with him about 4 weeks of age. Don;t put the females near him as they can breed at about 5 weeks themselves so essential they are sexed properly or you get a population explosion.
Mother is always right and she will cull pups if she cannot cope with or that she senses are weak or ill. Dad seldom does but in reality he shouldn't be there anyway as you don't want more litters.
You can't keep inbreeding them as this fixes and amplifies bad traits in. Some of these don't show till they are older so you won't know now if either of these two might develop glaucoma or diabetes will you. In the wild the young males are driven away and find their own territories and will not breed in to the same lines. In the wild also Campbells and WW live in totally different regions and would not hybridize.
Enjoy them as pets would be my advice.