Oh gosh, these two!
I’ve mused a bit about Chase’s knack, since he’s easier for me to write. Chase would have a natural charisma, an ability to influence the emotions of those around him (think Mantis from Guardians of the Galaxy, except he doesn’t necessarily need physical contact). It’d be a good way for him to keep the peace among whichever group he’s in, or, if he can manage to get close enough, make a human tired or inattentive enough to escape notice.
Bobby was tougher for me to figure out, but @nightmares06 gave me a good idea. Bobby, since a lot of his insecurities are on how he measures up to others, would have a knack to borrow others’ knacks for a short time. Only one at a time, and since he’s not used to them he wouldn’t have as much finesse with them. He’d be quicker to burn them out than the actual “owner” of the knack.
Bonus: Chase’s little sister, Minnie, would have a knack to detect life. Very useful for finding out if a human is in a room, or seeing if there is a rat somewhere in the walls.