If all else fails, try moving your folk night to a different night of the week - tell your mates but not this lot who are spoiling the evening. When they get fed up of playing only to themselves, they will probably shove off somewhere else, then you move back to the original evening! This will no doubt require the co-operation of the landlord/lady but will be worth it in the long run. They sound like a right thick-skinned bunch and are obviously not open to subtle hints! Good luck.