Of the 3, I'd say Bellamy certainly has the highest chance of being an actual nakama, yes.
The whole specific dream to be a pirate, as well as seemingly nowhere to go post-Dressrosa, pushes him ahead of the other 2 in that regard. Also, the way that Bellamy said he could only escape the "great wave that was coming by getting on Doflamingo's ship" really sets up the opportunity for Luffy to use similar phrasing to offer Bellamy a place on his ship.
However, I still think that that chance of it happening is minimal.
Like you said, Bellamy has nothing while Barto and Cabbage still have their own crews to look after. However, judging by their moment together when Barto protected Bellamy from Dellinger, I wouldn't be surprised to see Bellamy join the Barto Club after all is said and done.
I agree that the chance is still minimal, and I'm unsure at this point if anyone in this arc will become a crew mate. Besides the three that I posted, nobody else seems likely. Rebecca's desire was to be with soldier, her father, and once this arc ends she'll get her wish. Kyros won't leave the kingdom and Violet will probably want a peaceful life after what she had to go through. Sabo is obviously a no go because of his position, and the rest of the coliseum fighters don't seem likely, since they are criminals or belong to various countries. Law will only stick around for the alliance, since he has his own crew and wants to be the Pirate King.