I don't think he was a good brother in his past life either so he'd definitely stay as a villain
honestly the royal couple is just really dumb. i wouldn’t count them as villains. they’re just really easy to influence. you can see that in how they just end up doing what the people around them (the real bad guys) tell them to do. even if the brother regained his memories, he’d keep being immature. it’s clear he doesn’t like his sister, but it’s more of a childish inferiority complex then a conniving villain.
But one the reasons that mc has this kind of life is also because of his brother so I think it can be attributed to guilt
would it be funny if one day the emperor regained his memories and realizes the mc is his sister? or if like a bonk to his head triggers a memory and then suddenly he wasn’t a villain anymore