Don't want to discourage you from learning Rule Machine, it's a worthwhile investment. But for controlling exhaust fans based on two humidity sensors, this app is (IMO) the best. It's not in HPM yet so you'll have to install the code manually.
[APP] Smarter Humidity Fan FORK for Testing - 
Custom Apps and Drivers / Custom Apps - Hubitat
Don't worry about the "for Testing" thing in the title. It's been "in testing" for 2.5 years now, perhaps the longest test period of any Hubitat app known to man. It's quite stable and works very well.
