Where is Kafin's brother?

Kafin Lowlance says that his brother got abducted by an Oni when he moved to Waterdeep. He wants to find his brother.

Kafin about his lost brother: "'So shortly after we left our village, a week, I think, we settled down in waterdeep with the egg that was my brother. When night came upon us we heard a knock on the door, an injured aarakocra back from our village also wanted to settle down in waterdeep, but had no shelter for the night. We gladly welcomed the darned thing in. And as night came I was woken up just to see this horrifying creature leave with my brother. Everyone saw it but no one could do anything'"He was still an egg when we was abducted.