There are quite a few different views on keeping pairs of dwarf hamsters
. Many feel they shouldn’t be kept in pairs as it’s so common for them to fall out and need separating. Breeders are often keen on keeping them in pairs and know how to do it successfully mostly. Some people do manage to keep a pair together for life but it’s not that common. Some breeders will say Roborivski hamsters do better in pairs more than other dwarf hamsters.
You have had a hamster before and knew how to set up the cage for a pair so if you want to try it I think that is a choice- but as the others say you always need a spare cage in case you need to separate them quickly. Any sign of squabbling can lead to maiming or death. Some people feel they should never be kept in pairs as there have been some horrible outcomes- but if you’re aware of what to look out for then I can understand why people want to try keeping a pair. If you do have to separate them then you will still have two hamsters but they won’t be able to be out of the cage at the same time for handling (unless in different rooms). Whereas when they live together it’s quite important to take them both out together or one can get territorial in the cage very quickly if the other is taken out for handling.
So it’s one of those things where there are different views. Technically it’s not necessary for them to live together- but a sibling pair can - as long as observed carefully.