What i am trying to say is that if Hiro and co’s actions in the present, that resulted from his jump to 2012 and meeting himself in a future where Sylar isnt dead and the bomb went off, have altered the future so that the bomb didnt go off (but sylar is still alive) - would future Hiro and co and the resulting events that happen in a second alternate future (with no bomb) be enough to make Hiro come back and still do the same things he did in the final episode? Or would that change things to a third alternate future and thus a perpetual loop of alternate outcomes and ever changing futures?

You know what, its only a TV programme.

When “future” Hiro is surprised that “present” Hiro is there is because he is actually the future version of Hiro from the timeline where Claire is not saved. He must have gone back in time to before the events leading up to the explosion began then gone forward in time again to be able to be around in the current timeline. You say he pushed himself out of the current timeline. I think it’s more like he is from an alternate timeline and he pushed himself into this one.

Concerning Charlie, again it’s because he goes back in time that he changes the timeline. The Charlie that they meet at first is essentially not the same Charlie that he goes back in time to save.