People have reported only the host getting the achievement (in general and for this one specifically).
If you have access to the Hall of Darkness, maybe the host can try the game in single player, respec, boost something to 5 (whatever you have the most spare skill books for), visit the appropriate elemental in the homestead to buy more skill books, or Arhu or the traders in Silverglan or Cyseal. After I posted last night, I did that with Geomancer, since I had a late game save with a few earth spell books, and could visit Peat and Arhu to get to 12, and unlocked the (GOG version) achievement.