He should file trespassing charges on'em. But the police obviously ain't doing their job in the first place if they can't get them out of there.
Me personally, they'd get one warning, then that guy sittin' on the counter with his foot on the sink would feel my wrath upside his head, job one, then I'd commence to clean house with the rest of 'em and deal with the fallout whenever, whatever.
I don't kowtow to anybody, no matter what might happen, especially a bunch of punks.