[cypher]

If there's a big difference in weight then it probably would be best to separate them, it is quite a common problem with pairs, one grabbing all the food & preventing the other from getting enough so it would be better for both of them.
I would just give them a chance to settle & put a few extras in the cage for the thinner one, porridge is really good for hams but I've found Russians aren't always keen on wet foods, a big favourite with mine has always been the baby cauliflower cheese (4 months or under) none of them can resist that! Probably best to just stick to more natural foods like mealworms, sunflower, pumpkin, hemp & flax seeds, tiny pieces of nuts, maybe a little piece of plain chicken now & then. Once the thinner one is in it's own space with no bullying it should begin eating & thriving much better.