The 'nuke' is the Wrath of the Patriarch spell (the only level 1 skill you have). It is used like any of the other skills; get close enough to highlight a nest or tower and hit the assigned hotkey (as long as it is not during the cooldown period and you have enough mana).
Just pressing various spell keys isn't quite as selective as you need to be.
Ygerna and Behrlihn presumably took a one way (this time) trip to the Hall of Echoes.
Like Divine Avenger said, the techniques that work in nightmare mode are the same things that will work in casual. The difference is that that casual should be more forgiving of mistakes and less than optimal strategies.
