are you broadsiding with the ship? keeping the arcs overlapped on your target? Sometimes its a visual bug in the fx render if you don't see them all firing, have you got all them firing via the weapon tray i.e is the cooldowns cycling.
I run a macro on my g13 that presses the space bar every .5 seconds as that from what i notice helps alternate the firing sequence of all phaser arrays on my cruiser since they have a 1 sec cooldown per cycle and gets them all to fire properly when broadsiding.
Depends. th3xr34p3r asked some questions and we need to know the answers for us to help you. Explaining with specifics about your ship build would also be helpful.
I have (I can;t log into the game form here so I can;t provide specifics) three dual cannons and a torpedo up from and 3 torrents that can do 360 degrees in the rear. I can usually fire with all weapons with a target in front of me because it;s in my arc. If a target is to the left or the right, all I can use is the back turrets because none of the forward firing weapons can see the target.