Nope. He only fell in love with her after she killed him. He became like a spirit attached to his sword and followed her around, and slowly he fell for her. Her family was picked cause they had no connection and were considered irrelevant. They didnt expect her to become super powerful after becoming possessed and unbeatable.
Damn, you on the right track but it's even worse. The above comment is half right. Yurien fell in love later. BUT. Her family was targeted exactly because Yurien glanced her way for more than 5 seconds at a ball (he saw her soul was brighter than others and was curious for like 2 seconds). The fucking second prince went through the whole thing just because his brother showed a 5sec interest in her.
……….I know why they targeted Her family. I bet It has to be because Yu-dude whatever his name, liked her and the vindictive trash who plotted this was going for two birds one stone.
Not only to bring glory to themselves by defeating the cursed sword but also dealing psychological damage to the 3rd Prince by massacring the woman he loves whole family.