Abi, at the end of the day, you really did make the right decision here for their sakes. The consensus is, that Chinese hamsters are very much solitary hamsters much like Syrians are, but pet shops keep selling them in pairs which is criminal. I would go as far as saying NO hamsters should be sold in pairs unless the person keeping them is a breeder and knows what they are doing and has a learned knowledge of the species, like Vectis does.
Female Chinese are even more unpredictable than the males! You can enjoy them now for their individual characters and don`t worry they won`t be worried about having their own space. The crappy cage will have a valuable use now, with or without the smelly tubes!!!!
And no, nothing you did was wrong. Changing cages can be enough to tip the balance with pairs a even if it didn`t happen now, I would bet on it that you would have had to separate them at some stage, so it`s best it happen now while they are young and can now enjoy being individuals. x