Yamato is only
maybe likely if
@CoC: Color of Clowns Act 4 theory comes true.
Carrot is also a no. Simply because cared to do nothing with her character after WCI. Even robbing her of revenge of Pedro.
I think Carrot and Yamato are likely just because their dreams line up with Luffy's. That's the most important thing. Brook joined just because he and Luffy knew and loved the same Whale LOL.
Yamato and Carrot have had tons of scenes that show they are connected to the Dawn, like Yamato talking to Ace about Roger, and Pedro thinking about how Roger inspired him, when Carrot is fighting for Pedro.
The issue Carrot has is she chose revenge over what Pedro wanted. Pedro didn't want Carrot to take revenge. He told her that the Minks need to help the Straw Hats bring about the Dawn.
Carrot's quest for revenge is her being immature. She needs to overcome her desire for revenge, and realize that Pedro wanted her to help the Straw Hats bring about the Dawn, not hate Perospero. Which is why Perospero constantly complaining that he's getting blamed unfairly is so funny, it's Oda literally admitting Carrot is wrong for blaming Perospero.
Pedro killed himself to save the Straw Hats and Carrot. Perospero had no intention of murdering Pedro. Hell, after Carrot tried to kill Perospero on Onigashima, he spared her life. Perospero is not a murderous person, he's generally a good guy, look at him give kids candy and then tell them exactly when they can eat the candy coaster he made. Perospero IS like Pedro, an intensely loyal person who would do anything for his family.
I honestly think the reason Oda paired Yamato and Carrot together is because they're both very immature, and are so focused on their mentor that they've lost sight of themselves. They both need to fix that before they can become Straw Hats. Yamato is obsessed with Oden's legacy, and Carrot is obsessed with Pedro's. They both need to grow up and become their own people.