AvA/AvM fandom is literally the best fandom of all. Like can headcanon character relationships however you want and everyone is okay with that! (At least most of fandom..)
And without going too far:
-You can headcanon that they're all siblings or just hollowheads are siblings or just colorgang are siblings or they're all just friends or you can ship them one by one or THEY'RE ALL POLY DATING MAYBE
-You can headcanon their genders whatever you want
-You can headcanon their ages differently too!
And for example, I don't headcanon anyone being siblings but I do enjoy AU's that they are :D
I dunno I just love how it is :P