According to the section on the Aether II's github page 
"If you're wanting to create a gameplay video/review, extension or addon, parody, or any other fan work of your own for the Aether, go for it! We love seeing the content our community creates, and we hope to make it as welcoming as possible for everyone.

... All assets of the Aether II for Minecraft 1.8+ (found in the resources folder) and Wiki contributions are under the CC BY-SA 4.0 license unless otherwise stated."

The linked creative commons is located here: https://creativecommons.org/licenses/by-sa/4.0/

This project is contained under fair use for textures hosted in the Aether II mod.
The remaining textures are customized and inspired by the Aether textures and features, not direct copying of textures.

https://aether.fandom.com/wiki/The_Aether_II:_Genesis_of_the_Void
https://www.curseforge.com/minecraft/mc-mods/aether-ii
Version used: Mod version for minecraft 1.12.2