sorry guys, but you'll have to only include the characters who knew about Luffy's dream, because Luffy told his crew about his dream, which closes the door for those who didn't know about it, this leaves four characters:
Shanks: he's a Yonko, as the captain of his crew he can't join.
Sabo: as the second in command of revolutionary army, he won't join.
Reighley: as a retired pirate, & right hand man of Roger, he won't join, I mean he even knows what the One piece is.
Yamato: Yamato is the only logical possible candidate, so it's either Yamato join SH, or no one joins.