Yeah, the first bit reads like a prepared guard protects you and your champions, and an expended guard protects just the champions:
Guards that are prepared
protect you and your other Champions. While you have a
prepared guard in play, you may not be attacked, and your
non-guard Champions may not be attacked or targeted by an
opponent until all of your guards are stunned.
Of course, this contradicts the later bit in Attacking
To attack an opponent, subtract any amount of Combat from your
Combat Pool and lower your opponent’s Health by that amount.
Opponents cannot be attacked if they have a guard Champion in
play -- you’ll need to stun guards first before you can attack the
player they are protecting.
I'd probably play it like Star Realms until we get this sorted out: combat must be spent on guards before non-guard champions or players.
(With the expended/prepared bit a visual reminder that abilities have been used this turn.)