I sometimes joke that that easiest way to tell the difference between English girls on a night out, and prostitutes, is that the prostitutes will be wearing more clothes ;)
It would be weird for two English girls to be operating out of an RLD pub as amateur prostitutes in Amsterdam, sounds a bit like the proverbial
Coals to Newcastle situation. Possibly they were more interested in something closer to swinging? Or one of them was trying to score some coke / disappearing off for a "cheeky line" or something? Or maybe they were just drunk. Drunk English girls are a marvel to behold and could get up to just about anything....