Okay Thereshow, concentrate on picture no 2 from the last set you posted- you need to find the ceiling rose nearest the one to the bathroom, and hopefully, the one that supplies the bathroom setup. This shows 3 live wires, on in, one out, and one to the switch. As you've only got a live and neutral in the bathroom lights, they've had to set up a junction box, take a live and neutral to the JB, and then take the live down to the lightswitch. The switched live comes back to the JB, and then the switched live and neutral goes to the bathroom light. So from that JB, you need to take a 3 core and earth, pick up the live, neutral and switched live, and take them to the fan isolator, and then to the fan. Correct me if I'm wrong guys.