So Gem Harvest will have a mysterious character that is supposed to be relative to Greg since he does have a same nose as Steven and Greg.
Which bring me to this question
Why Greg never mention about his other family member beside his uncle and his aunt?
I might be wrong on this but I think there was a BAD BLOOD between Greg and his family because maybe his family are aviators and he wanted to become musicians but his family against the idea of him being musician but apparently his uncle and his aunt supported him and encourage him to follow his dream.
That's explain of why Steven doesn't have his grandparents come to visit him or maybe they're dead like Greg's Uncle and Aunt.