Sanji: They are after Momo and Shinobu-chan!!
Sanji: Who is Young Master Yamato!?
Sanji doesn't know how strong is Yamato and he knows that momo is more important than the red scabbard, my guess is he's gonna choose momo.
Let's not forget aswell that king insisted a lot in taking down momo as he's the most important man to kill. King might even try to kill momo himself at some point.