[cypher]

Usually if you see a big difference in weight with a pair it's because the more dominant one is preventing the other from getting sufficient food or is taking the best most nutritious food, that's not necessarily something you would see happening as hamsters tend to take food & eat from their hoard mostly, the more dominant one could be taking the others hoard or could just be preventing it from getting the food.
I wouldn't say Ernie is overweight at 65g & you can't put a ham on a diet anyway, only encourage more activity if they do get overweight which is quite uncommon, he may just seem big in comparison to the other who is still a small size, they do vary in size but with a pair I would be more inclined to think that the other is just failing to thrive, grow & gain weight as he should, if he is getting stressed by the other more dominant one that could add to the problem & prevent him from doing well too.
Personally I would separate them, they aren't social animals & do better alone in their own territory.