Ok, so how do 2 people from opposite teams look alike?
Simple, some are clones, some are original
In the beginning, there was one class per each team.
There was only a Blu Engineer, Blu Soldier, etc
There was only a Red Heavy, Red Demoman, etc
Now both teams saw how threatening the other mercenaries were. So they decided to clone the entire team of the opposition.
Have you noticed in the webcomics, when a class gets a backstory, its
only from one team(although this is justified). No backstory for the RED engineer, just BLU. No limelight for the BLU demoman, only the RED. And unless They make comics for them(which, in hindsight, would be stupid) , it proves my point even further.
If you wanna PM me, send it to my mrsunshinesprinkles account; this one is blorked.