If Jonathan Joestar didn't die on the boat, would he have eventually developed Za Warudo as a stand? I mean, Dio was using his body in Part 3.
He would probably have died of old age or against the pillarmen by that point.
No, Za Warudo wouldn't develop without the stand arrow, which wasn't in the US where Jonathon was moving to.
But didn't Joseph and Jotaro develop theirs own their own?
no, stands are linked to a person's spirit. all that was left of Jonathan was his flesh and genes
Only because of their common heritage with Jonathon. Shit's really inconsistent, but basically descendants of stand users often develop stands while random people like Jonathon would need the arrow to develop them.
No. When Dio got his stand, all the Joestars got a stand too, or at least they did teorically.