So many places! I'd avoid the dance clubs or places that are too crowded with letches and go straight for the gay ones!
How about:
Dinner at someone like Otto in Tünel (Italian, relaxed, inside) or Sanat in Nevizade (rooftop, Turkish) or reserve a big table like in House Cafe Tünel.
A cocktail or 10 at somewhere with a view like 360 (near Tünel end of Istiklal) or Mikla (Pera next to Tünel).
Then 3 (new gay club, no straight men allowed in Galatasaray).
Depends what type of ladies you have and the kind of action they are looking for!
Where do they live in the UK and where do they go out, what are their jobs? May help.
I'd consider taking them to a Bos club as for any visitor, to party on the Bos is just fantastic and what sets the city apart from many others. You could have a dinner in Ortakoy, pop to Angelique and reserve tables at Reina (to avoid the entrance fee).
Maybe they want dance music, student 80s/90s music, guys and noise but not expensive - in that case I'd do the Nevizade, Tonique (Balans roof) and somewhere full of men like Mono (hate the music/too small but many like it). Depending on how many there are, try and talk to the owners/managers (can help you on there on the above).
If they want to get dressed up then I'd avoid doing many of the Beyoglu bars and clubs as they'll just get hassled.
However many people like that. Hen nights always attract attention!
How many chicks are there?