Galba was certainly a member of the royal family. If his play for the throne was considered worthy by posterity, then there could be implicit acknowledgement of that in the New Testament.
You must be correct in assuming that the three men crucified by Titus (as described by Josephus) represent important royal/political figures. They could in fact correspond to Galba, Otho, and Vitellius as you also propose. However, it isn't clear why one of those three is depicted as surviving. Perhaps Galba or one of the other two short-lived emperors was not literally killed. It may have been necessary (politicaly correct) for Josephus and other contemporaries to disrespect the memory of Galba. Prior to the reigns of Vespatian & Titus, Josephus may have been close to all three, and found a way to memorialize that in the story of the three on the cross.
It's less likely that the cult following of Galba lasted very long. The only two royal lines that seemed to matter in the long run were those of Jesus and John the Baptist.
Responses To This Message
© Charles N. Pope, US Library of Congress. All rights reserved.