Had a conversation about pronouns in Welsh, and it briefly touched on formality. Got me thinking about which of us would use formal/informal pronouns for eachother. Honestly, we're generally chronically informal with our speech. But on the other paw, our instinctive second person pronoun in Welsh is formal. But our instinctive third person masculine pronoun is informal. Together I guess it does paint the picture of being cut off from the language as a child.
Thinking about the intra-system relationships on this level is interesting though. I'd use formal pronouns for Echo I think, it's a much more powerful fae. But otherwise, what, I think Spoke might just generally use formal? Maybe UMBRA too? UMBRA would definitely use whatever someone asked. User configurable terms of address. And like, the rest would probably be mostly casual. The pooltoy might slip into formal talking to a shark without even realising it... that'd be cute.