It's not unreasonable for Amberser to suspect a conspiracy. When he stepped out of his role as a member of the Elegy Poetry Society and took another look at the organization, he began to feel that something was inherently wrong with it.
Yeg was selecting a successor for the Grim Reaper, but what does that have to do with the undead?
Apart from Yeg, the original Grim Reaper, was there any other Grim Reaper who was undead? Including the current Grim Reaper, Kranvo, he was a human, not deified in undead form.
It was already illogical for the Elegy Poetry Society to only choose the undead. There must be some hidden factors, which Amberser could not clearly state, but with his friends' safety at stake, Amberser felt compelled to consider the worst.
This was also the "trouble" of being reincarnated as a human; Amberser needed to start thinking about those around him, rather than treating them as a Lich would, seeing how much Gold Coin they could produce.
