@Fwelin
That seems like exactly what a “raised by a sibling” child would experience too. They’re family of some kind, and Twilight was probably Spike’s official guardian despite her age. But there isn’t a defined relationship for either of them, and it’s troubling to both of them. She’s not his mother, but she kind of is because she largely raised him and he has no other parent who’s more of a mother than Twilight. And she is kind of his older sister because she was hardly mature enough to be his actual mother (even aside from the species difference), but kind of isn’t because she in many ways had to be more of a parent than a sister.
So I think that is exactly why it was frustrating to Spike too. She would always be somewhat of a sister rather than a mother, but could never really treat him as an actual sibling because that would be abandoning what’s actually the more important half of their relationship, especially when they were both very young. Which would set a pattern for later.
