Ilike the idea of Simon being Marceline's godfather/Uncle who got institutionalized
Ash was some 20 something who Marceline dated like the Skyler/Shelby relationship from South Park Cat Orgy
Tree Trunks is a nice old lady who makes pie.
James Baxter is some senile old man who only repeats his name, who ride unicycles and stuff to entertain kids.
Huntress Wizard is some fierce hippy chick who's in college who wants to be a botanist, or just a senior in their high school who wants to be a botanist.
I'm pulling stuff out of the air.