Your warlock should have a minimum of 24 AC (10, +5 level, +4 stat, +2 armor, +3 magic item) which goes up to 26 as soon as he acts (shroud of black steel. Does the ranger really get a +20 to hit? By my count he should only have a +16 (+5 level, +5 stat, +3 prof, +3 magic item).