I'm looking for a manhwa where the Female lead is part of a royal family but was neglected by her father and she killed her brother. When she returned back to time she decided to live peacefully and let her brother be the king. She doesn't show emotions except for when it comes to the one she loves idk if he's the first lead but he was friends with her brother and has black hair. The story is still on going and the characters are still young. It also has a second lead blonde haired guy.
Could this be The Tyrant wants to be good?
The story fits your description very well: the female lead was neglected by her family (which is the royal family). She kills her brother to become the ruler, gets executed for her tyranny, returns to the time she was a child, decides to live a good live and let her brother be king. The guy she loves has black hair and while she is not emotionless, she shows very little emotions with everyone else than him.
The big difference is that she and her brother have blonde hair, not white. It has been some time since I read the first five chapters and I can not remember a third male character in their age group, but the cover shows another man with white hair.