The Matchmaker Gets Matched!

I brought the slowest couple in the universe together and finally got them engaged, but they called the engagement off on the day of the ceremony itself!
I was reborn as the male lead's younger sister in a fantasy romance novel. But the female lead's older brother, Aiberg Rafaello, has a severe sister complex and would not let go of his sister.
So, how do I make him stop obsessing over his sister? Find him a love interest.
"What kind of person do you like, your grace?"
"I like someone with blazing-red hair and eyes like the flame, a lady who never stands down for anybody. Speaking of which… I'd say you match the description." I was only trying to save the lead characters' engagement. How did I end up flirting with the female lead's brother?