I think Law wont join the main crew but just stay an allie though the possibiltie grows more and more with his sad back story and all though i still have my doubts. Jinbe will join no doubt in my mind unless he is killed off whick i dont think so. Maybe he will be killed off as a SH member which would be interesting to see. Now for Hancock and Ceasar i think your theories are kinda weak there is no real indication or foreshadowing its gonna happen and honestly i dont see them fit if Hancock joins there will be romance on the Sunny which doesnt want for One Piece so i dont think thats gonna happen and Caesar was just a too big of an enemy too join really. He was the main villain of an arc and most of the crew hates him.