After reading the comments I think the brother knew from the beginning. The chapter where you see his thoughts (ch 17) he explains his regret and wanting to fulfill her wish. Like he makes it apparent that he knows his sister is gone and she made it really clear in what was obviously her farewell to her brother. Like for sure he knows and he's sticking around and treating the MC well because it was his sisters final wish. I hope we can see more of what the OG Peony did and more of her life before the switch in later chapters.
After reading the comments I think the brother knew from the beginning. The chapter where you see his thoughts (ch 17) he explains his regret and wanting to fulfill her wish. Like he makes it apparent that he knows his sister is gone and she made it really clear in what was obviously her farewell to her brother. Like for sure he knows and he's sticking around and treating the MC well because it was his sisters final wish. I hope we can see more of what the OG Peony did and more of her life before the switch in later chapters.