Script for humidity fan

Hello,
Would anyone be able to help with a script,

I have a ventilation fan that I want to increase to a maximum when the humidity in the bathroom increases more than eg, 5% (a relay is energized) and the lights are switched on there, and then turned off when you go out and turn out the lights, has 3x bathroom so the fan may not turn off if there is any person in those other bathrooms.

//Jens

[jay (support)]

Gonna need to provide more detail - like what are the exact device types involved and how they're controlled. Also, I get the first half of your description, but get lost in the second half.