Mate, he is your only honest worker by the sounds of it, they all are tossing it off guaranteed!!!. Id make sure they arnt doing there own work on the side if i was you!.
Sorry to throw a spanner in the works but having them work 7.30 till 3pm id expect at least £250/300 to be cleaned not a quick £150! I can bang £150 out in a few hours..
That lad who you think is taking the p is actualy your best worker.
Id seriously get rid of 1 of them and up the other 2's work load upto £250/300, less overheads and more profit for you.. Win win.