I have no idea to be honest but I imagine it depends not so much on the hamsters (brother or sister pairs) but their environment (cage), how large/small it is, the way it`s accessorised (i,e...not changed around too much or at all) and their individual characters. Pure bred winter whites are beautiful but finding a breeder with long term status might be the problem. They could then give you more details on their lines and behaviours.
Anyone who wants a pair of dwarf hamsters can always give it a try, but most end up separated sadly. Robos seem to be the worst culprits! I wonder why....
Pairs probably rely on one another for company and enrichment, so human intervention may well be one cause that interrupts that harmony if they are handled a lot or separated. Stress/upset of balance could tip them over the edge. Many people who have kept pairs report that they can be scatty or don`t like being handled. Or one is fine while the other is nervous. One could be dominant over the other too.
The rules that apply to keeping pairs can be all well and good, but whether it`s enough to keep them together is the question. x