Rather then Bathroom Fans, consider a Whole house Unit. They can be rather inexpensive & They do what bathroom fans & dehumidifiers do, only better.
I've used a unit called a "Quietvent" to solve similar problems. You can receive info on such a unit at:
DEC International (R/C) P.O. Box 8050 Madison, WI 53708 608-222-348422-3484
They have a flyer on the unit that also gives a simple setup (If you check w/ a local HVAC, they probably have the same flyer). They only addition I would suggest is connecting the low speed of the unit to a dehumidistat. This runs the unit based on actual humidity, rather than trying to guess with the included timer.