Some people pointed out that the whole story depends on the twins being incompetent morons/bratty children for the story to be able to move. As characters they work, even if i myself am not the biggest fan of Adras, but they sure as hell don't work as the main enemies of 3 games.
They are stuck in a limbo where they cannot develop too much because if they become competent they don't need Rowan, but as they are they would at best be the prologue villains that get defeated to let the real threat arrive.
In act 1 Rowan already has the loyalty of some very important people, the goblins that fill the coffers with money, the one guy making all the equipment, the mistress of the sucubus and the guy that knows how to get the beasts to obey, and the starting of loyalty from the strongest mage on the castle, the most loyal servant of the previous demon king saying he is the true strength behind the twins, a somewhat friendship with the fey emissaries and the affection of the spy mistress.
Now comparing with the twins.
Both are spoiled kids that act like it and are not immediately defeated because of natural ability and not capability, Adras survives his battles not due to him being a good strategist or warrior ,but because he, being a half demon, is super strong and regenerates faster than he can get his face smashed in, and Jezera thinks she is a master spy mistress and corrupter, but if not for her lovers capabilities and her daddy's name she would be not better than your average noble girl putting afrodisiacs in food
I imagine something is going to happen to shake the status quo, but so far they are somewhat one note, Adras has the mother of all daddy issues and a superiority inferiority complex with Rowan. The effort he put in trying to prove himself the better man makes me believe his insecurities are real and will be used against him.
Jezera on the other side shows time and time again she under estimates Rowans abilities to run circles around her, and over estimates her own, if not for her whips magic she would be dead in the prologue, and the way its set up now she is one scene of Rowan discovering more about the neclaces than her from becoming the one having the tables turned