To what extent are Momonga's underlings aware that he's "from a different world"? Albedo's conversation with Momonga at the beginning of episode 5 has a few elements that confuse me. Albedo reports to him that they have yet to find any other "Yggdrasil players". Later, Momonga tells her that her love for him is a result of him messing with the "settings" Tabula specified for her. 

Does this mean that Albedo is aware that her entire world used to be just a video game from Momonga's perspective? Did Momonga tell her this, or did she inherently have this knowledge from the very beginning (i.e. when Momonga got transferred into the game world)? Do Albedo (and the other underlings?) just not care about this?
Short answer, they see them as gods, so they probably think they have their own sort of "heaven".  Long answer, they do know that there is a clear difference between the underlings and Ains (He ordered to be called that, so that's what I'm calling him), we see that they often overheard things they were talking about and associate it with god powers, just to drive home how powerful they think Ains and the creators are.  Ex: I can't speak for the manga, but in the anime, Demiurge overheard some of the creators talking about their jobs, to which he associated voice acting as actually breathing life into inanimate objects.  You also have to remember that they had to behave as regular NPC's before the servers shutdown, and in that time, they literally could not do anything unless they were ordered to.  So, although they do realize Ains is from another world, but I doubt the image they have in their heads about the "different world" of Ains is very accurate.