My boys share a Switch at home and I wanted them both to be able to join my Realms world. Either can join independently but if the other tries to join via split screen I see them log in as "Steve" (I assume since they are in Minecraft via the other brother's account) and the Switch version goes down encountering an error. So my question is ... is it possible for them to both join my realm at the same time via split screen mode from a single Switch? 

It seems like this/a similar issue was reported here (MCPE-56288) and marked as "resolved" although it seems that the bug still exists.