Were all the heroes in Overwatch part of the original Overwatch organization?

As I understand it, the game Overwatch takes place a few years after the Omnic Crisis, where robots attacked and the group called Overwatch was originally put together to fight back. But for years, Overwatch has been disbanded, and only now it seems to be coming back to right the wrongs of the world.

The part that confuses me is that there are a lot of heroes in Overwatch who don't seem like they would have been in the original Overwatch. For instance:

• Widowmaker is an evil brainwashed assassin
• Dva is very young (probably about as young as you can legally get away with)
• Bastion is an Omnic

So, are these heroes supposed to have been part of Overwatch before it was shut down? Or, if not, who was in Overwatch originally? I assume Winston, Tracer, and Soldier 76, but what about the rest of them?

Solution 1:

Of the current roster, the following used to be members of the original Overwatch:

• Genji
• McCree
• Reaper
• Soldier: 76
• Tracer
• Mei
• Torbjorn
• Reinhardt
• Winston
• Mercy

Widowmaker technically wasn't a member of Overwatch, but she used to be Amelie Lacroix, the wife of an Overwatch agent. Pharah's mother is Ana Amari, a member of the original Overwatch strike team although Overwatch was disbanded before Pharah herself could join.