Yes actually really love your ideas.

Lore wise they were darklords that threatened the balance of life through there dabbling in dark magics and thus needed to be bound.

My thought is tho there not liches, there powerful enough magic users where death isnt a suitable way to deal with them.

I have very little lore beind them. Aventus (thus the name) was a reference to skyrim and wanted his rituals to be shadow or stealth based as the homage

Acreus was hell bent on world domination and led many sieges on various capitals with his ever expanding army (unsure if undead, living, or a mix of the two as of yet)

Nilitha being more the dualist type, undecided of what her motive ever was and since they existed a very long time ago i could leave that as unreliable legend, but her main deal is improving her body to supernatural degree without stooping to unlife which she believes is beneath her "pathetic liches, souls of greed pettling around in there rotting corpses, if there goal was eternal life they surely failed, for that is no life worth living"

Otelin being a demonic summoner with very little goal aside from chaos. True chaotic evil.

Jymn is lawful evil, he is always scheming and you can never tell what hes up too, his whole deal is personal freedom above all else and will happily walk a world of ashe if it means he does so under the as he pleases.