sorry to say this, its nature of hamsters. please my advice is do not keep them together. and do not forget to give them proper diet of eggs,meat,milk,yeast etc..
Hamsters should not be housed together under any circumstances. They are territorial creatures. When hamsters reach adolescence they will fight for territory. They need seperate houses. Eating is to keep the house clean.
Among grown hamsters, it's mostly a territorial question. The males compete with each other. If the young are eaten by their mother, it's because she can't provide for them.