Barrage and Skirmish Question!

So I'm a total noob but am going to run a one shot for my usual group so I'm just making I've got all the rules squared away.

If you Barrage you get two attacks so you could attack with you're main weapon and your heavy weapon (so long as it's not a superheavy)? Or you could attack with your main weapon and two auxiliaries so long as the auxiliaries are on the same mount? And If you skirmish you can attack with one weapon mount so if you say have two auxiliary weapons on the same mount you could attack with both? Like with two Nexus (lights)?

Sorry if this is a dumb question Thanks! Sorry if this is