The rules state you must have 8 members in your party. Which of these is correct, then?

1. You must play with eight different humans.
2. You must simply have eight "players" in the game, but they can be controlled by anyone.

If option 1 is the rule, how will this be enforced? Does every player need a SRC account?

nope

This means that you can have 3 SRC account runners and 5 runners without an SRC account.