Have you done any research on breeding syrians? Firstly you must remove the pups away from the parents to single cages. Syrian hamsters are solitery creatutes and they MUST be kept alone. These are onlt staying together as they are quite young. I have no idea why mum hasn't killed the dad. Females with pups will usually attack a male. Pups need separated in to single sex groups at 4 weeks and taken from mum. Males sometimes last longer together than females which usually start bickering about 6 weeks and need single cages. You need to start handling them as soon as the eyes are open. The little one is likely being kept away from the food by the bigger ones or he may have some sort of developmental issue. He should do well enough but I would get him on his own now and work on handling and taming them. We have a litter just now and we had a tiny runt who was hand fed from 11grams - he is now 100g but still a lot smaller than the others who at 7 weeks have been rehomes in to individual home. The females can and will mate with dad and siblings from about 6 weeks of age so I hope you are lucky and they are not all pregnant again.
Even if you have dwarf hamsters the male will mate with daughters and mum and you end up with dozens of pups so males must be removed at 4 weeks. Please get them all separated. They will go feral if you don't tame and handle them from young but now you need to start with each individual and tame them. This will take some time and devotion I'm afraid. You can see how we tame pups in the breeding board under 'The ketzinicos' Vincent our rund is having extras including oily seeds, baby food and porridge, egg, mealworms etc which he has alone in his own little box or spoon fed so we know he gets it.
The Ketzinicos