If anything, imo Smoothie and Cracker can be a burden for Kuri.
If the fight happens in manga and they are all in character:
Kuri is caring for his siblings much. So when King one shots Cracker, Kuri will get furious, loses his calm, and interrupts his FS. Then when Smoothie becomes large yet it backfires, she becomes easy target for the flying slash. Kuri will get even more furious, loses his calm more and interrupts his FS again.
Bringing those 2 non factors will backfire on Kuri. Yeah, 3 SCs aren't winning this until they dragged their mom to help them on this.