It’s very difficult to say who would have what knack! We’ve straightened out a few of the rules for their knacks, but each persons is completely unique. Siblings normally have abilities that complement each other, just like Sam and Dean. With no sibling, Jacob’s is standalone. The closer the siblings, the more their abilities complement each other.
Mallory would likely have something that would help her see into the hearts of others, while Walt would at least *want* something to help his family. That’s a cute thought for Bree! Very Alice-in-Wonderlandish.