How to eliminate advantages gained from the seating position of inferior players?
I think you can't have a serious, cutthroat game with a wide range of skills, so relax. Gently coach the new players, but no more than they're willing to receive. Play a couple of dummy rounds for the new players and then restart if needed.

If you're really serious, you can investigate ways to handicap the game, but that's really hard to do without ruining the balance of most games.