Teasing You with a Love Triangle in a Quadrilateral

I like my older sister, and Lu Wu likes her too. But she likes Lu Wu's older brother, and at the moment, his brother doesn't seem interested in dating. So the conclusion is clear: I absolutely can't let Lu Wu get close to my sister.

"Heh, Lu Wu, she rejected you again, didn't she? I told you she could never like you."

"Yeah, so I don't like your sister anymore, Lin Huan! I like you!"

"Get lost! I'm a man, damn it. Why would you like me?"

"I'm so used to you picking on me that I fell for you without realizing it."

P.S. This story has the protagonist marrying into his spouse's family. (Obviously.)