if i have a triggered burning sword on edric, win a POW challenge by 4 or more, does that mean i can't trigger edric storm's abilty since he is now immune to card effects, or does this mean i cna trigger it but do not have to discard him since he is immune to card effects?
Couple of things here: Burning Sword, like all other immunity, only makes the character immune to direct effects. Discarding Edric is a cost (you cannot be immune to costs) and the extra challenge is not something that affects characters directly. And anyway, a card cannot be immune to its own effects/abilities (right out of the definition of immunity). So triggering Burning Sword on Edric has absolutely no affect on whether or not you can trigger his effect. It's just beyond the scope of immunity.
Also, a question that i forget to get a clarification on. If i have a unique character stolen, then he gets killed can i play a retreat on him to return him to my hand? (i say yes, one other in our play group said no, was ruled yes, but just wanted to make sure we did it right).
The ruling should have been "no."
The text on Retreat is "Response: After one of your unique characters is killed, return that character to your hand instead of placing it in your dead pile." The word "your" always denotes a character you control (unless otherwise specified). When the stolen character is killed, it enters moribund, but stays on the table. The "take control" effect does not actually stop until the character is physically removed from the table. So when you would trigger Retreat to change the character from moribund(owner's dead pile) to moribund (owner's hand), you still don't control the character, meaning that you don't meet the play restrictions on Retreat.