The appropriate thing to do is simply to try to explain things if possible, and at least try the content a few times before deciding to give up.
Sometimes you'll be able to carry the rest of the party if you're very skilled yourself and the others at least make an effort. (Mostly possible in WP, occasionally possible in AK, but less likely in PS, HM HM or CBM HM)

They should augment the minimum required ilvl with recommended ilvl and minimum/recommended weapon ilvl.

Would be nice if there could be a way to measure actual practical skill level of players too, as ilvl tells you nothing about what the player is capable of in practice...
Some sort of solo skill challenges for each job maybe...