Welp, that makes... 1,2... around 4 people that know of Iruma's true race with Sulivan's consent (Sulivan himself, Bachiko, Balam, and Sulivan's butler (I forgot his name)) and around 2 that doesn't have Sulivan's consent
There are also those who are suspicious of Iruma like Amelie & Her dad
There's also one more person who also knows Iruma's identity; Alicrad-san (Iruma's ring), but Sulivan either acts like he doesn't know or he actually doesn't know at all
Alicrad definitely has one of the closest ties to the previous Demon Lord (Next to Sulivan of course), though we currently don't know to what extent