I want to play it out in game, so I just went with Caspian never really having an especially deep connection with all his spirit guides. The familiar can manifest when the character joins the game. I think it would be more fun if they didn't already know all about each other, but are attuned magically. I also had Caspian being able to read moods/ surface emotions with some effort, so the familiar could probably do the same,
Kindred spirits with disagreements sounds fun!
Ahaha. Yes, the Malaysian coral snake is very striking and beautiful, and deadly. Please don't bite Caspian. Being able to take him places without people necessarily taking notice is good! He can also be a crocodile skink - I was talking with the player of the air/ weather witch and we were going to do something where he rescues an abandoned crocodile skink on one of their hijinks.
Let's go with them speaking telepathically when the familiar is in his animal form, but verbally when he's a person.