Are weapons either single or dual wield in this game? Ex: if any enemy is using a mini gun, which i assume is a dual wield weapon, if I CRIT one of their arms, can they no longer use that weapon?

I assume you mean 1-handed and 2-handed weapons. crippling a limb on a living human spoils up their aim, but does not remove their ability to use that limb.

Dual wield is using 2x 1-handed weapon; one in each hand.

Edit: ghouls and synths can lose limbs altogether. while ghouls don't use weapons, synths do, and can lose access to features, like standing or shooting by limb damage.

Yes, this is what I meant. 2-handed weapons.

They drop it, nothing preventing them picking it back up unless they're a synth and you pop their right arm off.