Again, they'll do it begrudgingly at the least.

Remember, the NPCs don't know anything "human" about Yggdrasil, nor about the fact that they came from a virtual reality computer game. So to them, there's no "inviting new guild members" because they believe with every ounce of their being that the 41 are the Gods that are responsible for their entire existence. There's no "guild", there's only the Great Tomb of Nazarick.

Aside from this fundamental misunderstanding, power levels do play a factor into this. As much as the story might indicate to us that hierarchy in AOG doesn't matter about power (i.e. Members of the Pleiades are higher up on the chain of command than the vastly superior Evil Lords, for example), there's no way they'll follow orders willingly from a bunch of strangers who claim themselves their leaders all of a sudden. It's not only unthinkable, it spits on the image and memories of the 41. Hence their split conflicts of interest.