So are they gonna start going "good" like every other "evil" manga?

Lol... The word "evil" does not mean doing bad or immoral.. Some folk Religious people change it the way it is now....
Please do a research...

Bruh, the first chapter they already explained they weren't into war and conquering - they were/are focused on internal affairs. Also, like bogum said just because they are considered evil doesn't mean they're the bad guys.

think of it like D&D evil, it doesn't necessarily mean your a bad person. Just that you do bad things. You can to bad things for a good reason, or do good things for a bad reason. But evil here seems to mean it came from a place not considered 'good'. But what defines good depend on the world. But standard evil is like, murder, crime, hate etc.. But evil here seems to be more of a 'not of the light' sort of evil. But we all know the world isn't in black and white, most things are in a grey area but not all. So it really depends on what the author is portraying. Don't think of all good or evil as the same. At least this is how I see it.