We shall see who is right in the long run, perhaps. Seeing as how Kane apologized for disappointing everyone, has been indicted and is probably in negotiations to make this all disappear, we may never know.
I will say this, if the two brothers came forward and confessed they were worried because the doors on the cab were locked and the old man held them prisoner, I might change my mind. So far all that has been said is, it contributed to the situation. Since they appeared to argue about the money afterward, and then the fight ensued, it seems more logical to assume the cabbie had unlocked the doors by then. Oh and last, but certainly not least, if they were free to move about and no longer imprisoned as you put it, the proper course of action is to notify the police.
You go ahead and stick with your imprisoned story, if it proves to be correct, I will come back and wear the paper bag. If they were outside the car and assaulted him, will you do the same?