I recently went through the same process you are going through, and settled on six Columbia Falmouth Jackets (1XXL, 2XL, 2L, 1M). My thought process was that these jackets would be available in the event a guest found themself short a layer during a daysail and wanted to have something to fend off a light spray or chill air.
If I am doing a longer cruise or an overnight I suggest strongly that all crew bring a full set of their own appropriate foul weather gear that fits them correctly and comfortably. I take responsibility for providing harnesses, teathers, and pfd's -- the safety essentials -- they take responsibility for keeping themselves dry.
Otherwise you will go broke, and when the gear gets broken out you may find yourself with too few XL's and too many M's, etc.