1. Yes you can. If you have 2 actions, you can Charge for the first action, then take your free Charge attack. For the second action, if there is another model in Charge range, you can do the exact same thing.
2. The rules are vague on this one. But having played the Harbinger many times, if he dies I remove the Darkwings, because their rules state that even though they act independently of him, they are activated at the same time the Harbinger is.
Hope this helps.
SP