The Illuminati recruits Bluestone because of his determination. His unwillingness to give up his investigation into them was impressive.
Malone states Xanatos is a lower ranked member. The comics revealed he is rank 36.
Elisa tells Bluestone that she kept the gargoyles secret from him because it made her feel special that she was the only human they could trust with their existence.
Though Goliath implies Elisa planned to eventually bring Bluestone into their inner circle.
Though Goliath implies Elisa planned to eventually bring Bluestone into their inner circle.
While what Bluestone and Goliath were talking about was not revealed, it's implied Bluestone told Goliath his plan to trick Malone; which is why Goliath had the key to disable the Hotel Cabal traps.