Hi new guy here

[Havoc]

Make sure you uncheck the manual defensive fire optional rule and your defenders will fire as the attacker moves.

Not quite sure what you mean by firing all the guns in a stack... if you are firing during your turn, then turn off the artillery dialog box and select all the guns in the hex manually. Hold down the Ctrl key and a cross hairs will appear. Select your target by right clicking on the target hex. Otherwise, I don't know any other way to fire the guns together.