Basically, there two requirements to summon each Doll Knight:
- Each Doll Knight's Calling Bracelet must be on the person that will be protected. This is why Yae could not summon Doll Isamu until Dai found his Calling Bracelet (and Scarecrow took it and put it on).
- Each Doll Knight's master control trinket where the summoning words are uttered must be equipped. (This requirement is altered starting in episode 28.)
Doll Licca's Calling Bracelet is currently being worn by Rika. Her control trinket, the Calling Pendant, is worn by Nanae (Rika's grandmother).
Doll Isamu's Calling Bracelet is currently being worn by Scarecrow. His control trinket, the Calling Watch, is worn by Yae (Nanae's twin sister). (It's called a watch because it looks like one of the old-fashioned windup watches that is on a chain.)
(This is behind a cut because there's a spoiler about 10 episodes ahead.)
Doll Izumi's Calling Bracelet is currently in Catherine's possession. Catherine actually hides the bracelet in her clothes to prevent drawing too much attention to herself (you'll see it fall out of her clothing later). Her control trinket, the Calling Choker, is worn on Catherine's neck (you might have seen it).