atonement huh, who is this Andrea?

Andrea is their Older Brother who left for the countryside one day, It seems he has connections to the main leads especially the emperor and white haired guy.

Oh, I was thinking it might be their mother since it sounds feminine, but then I realized it could actually be their brother. Like you said, he indeed have direct contact with the emperor as one of the councilors. There's also a glimpse where the brother mentions he'll die or something, and decided to go countryside for unknown reason. thanks for confirming