I don’t know details beyond hearsay and what can be currently seen in the book. There has been an observation that characters have stopped referring to relatives with any term linked to family relationships. I can’t remember if Uncle Chuck is exempt from that or not without pulling out the books themselves, but I know there was a scene not too long ago with Tails feeling upset and his father going to comfort him without any reference to familial ties.
It’s handled well enough where you don’t quite notice it but when you’re aware of it it becomes one of those ‘Huh. That’s weird’ moments.