With regard to devourers killing the goblins, I don't the devourers serve the Absolute. I get the sense that the Absolute might be something somewhat separate from the mindflayers as a whole. And even if that's not the case, then the goblins certainly don't know they're serving mindflayers and would probably attack any intellect devourers, and the devourers would logically defend themselves. So that at least makes sense to me without any difficulty.
