Okay. As a rule, I don't do crit confirms. If you roll a crit and it hits, then it's a crit. A natural 20 always hits and always crits. Just a personal thing, for that's how it was for me, playing with my DM uncle.
Yes, unless you have evasion or improved. Then it does none.
Also, while we never set an initiative for this fight, NMC rolled 3, Xavier 16, and Allen and Allison haven't acted after acid spewing.