I also reworked some ideas for both Hyper!sans and Arch!sans:

Both characters try to keep the infinite amounts of universes in the multiverse stable in different ways.

Hyper!sans:

tries to give Aus more character and originality so that they are intresting and unique. He is also a very fun and playful prankster, he just uses his powers to goof around and have fun.

Arch!sans:

on the other hand tries to maintaine a certain level of order, so that the universes wont spiral too much out of control. He is a bit edgy, and likes to scare people for the heck of it (pun intended)

They both are needed to keep everything under control

Their relationship?:

Both are twins and and their relationship shows that. Bassically they tease eachother and argue alot but still care for eachother.

They'll both have different ways of handling with the 4th wall and other stuff that comes with their positions in the multiverse