Procs with normal weapon attack?

So if a skills says it has x % to proc on normal weapon attack and you have 2 skills that do so, do you have a chance to have both proc at the same time or does one proc and you lose the other.
If you lose the other is there any reason to take more than one proc on normal skill?
Example inquisitor 20% to proc with ranged weapon. is there a point in taking fire and cold?
Also if you are using a demo as your secondary class would fire strike “stack” with the proc or be replaced by it?
If you are duel wielding pistols does each pistol get a chance to proc ?

Thank you guys I’m sure you’ve seen a thread like this but I can not find the info.

Zugs

See post Weapon Pool System (Chance to use an Attack) for more info.

KEY: For duel wielding inquisitor pistols.
Main hand : R
Off hand : L
Both Hands: B
Bursting round: br

it would be something like this:
brbrbrbrRRRLLLBB
were as the chance to use the skill is 20% of every attack (main or offhand)?
and the Demo skill fire strike would stack on top of all those attacks?