well for one, it's intentionally ambiguous for poseidon to pass of as clement. the mc has no reference to recognize either of them and would reasonably conclude that was clement who passed the hotel for him once he learned of the story. i forget the exact wording but try and reinterpret his story as someone who lived his younger years in ancient greece and regrets failing to prevent his son from being sentenced to the hotel. keep in mind poseidon is meant to be a bit senile when you meet him. i don't know if asterion would know, clement just kind of rushed everyone out. not sure if he even went through the process of becoming the new master. also he's been stuck to that room you find him for 80 years. he probably was too numb to feel anything.
as for pedro, he is like middle class, that's very different from being so rich you could burn piles of your money and still not have to work a day in life anymore. there's a huge shift on your sense of purpose, when getting money is no longer a motive for you to work and do things.