I would guess you can, but one big fan will work more efficiently than 2 small ones. I can't say for certain without seeing in person.

"energy_rater, if you vent the humid air from a bathroom to the soffit, what's going to keep that moist air from going right into the attic?" back draft damper attached to bath fan housing. venting attached to back draft damper. venting exits soffit to exterior. fan being on will push air out of venting, venting to exterior of attic will keep moisture out of attic. also, if you ever take off the cover of the bath fan from inside the house..there is an oversized cut in the ceiling that is covered by the cover of the bath fan. sealing this cut is recommended to keep attic air/temps/ insulation particles out of houses. I use Hardcast brand mastic tape #1402. I also use this tape to attach back draft damper to housing of bath fan for air tight seal, and to attach venting to back draft damper. best of luck.

Thanks for your thoughts. The vent levers to the outside wall were opening fully when the fan was on, thus eliminating the possibility of 'stuck levers' or any thing disconnected as being the problem. So, I called Broan and spoke with a man who said it sounded like the motor wasn't doing it's job and in spite of the fan being out of warranty, he was very generous in his offer to send a new motor at no cost. I'm a Broan fan for life as a result. On Monday, our handyman is coming to install the new motor and use spray foam around the opening to the attic which should eliminate the 'attic smell'. I think that sealing up this gap will also improve the fan 'draw'. I can always count on my Gardenweb family to come to my rescue ~ thanks for your time ! gardening annie

Some of my info will repeat what has already been written. In the first photo: It looks like the duct is looped around to go behind the fan and then it goes up to the roof to exhaust. I would have rotated the installation of the fan housing itself to give a shorter path to the exhaust boot. 2) Rigid duct is better than flex duct. The wire coil in the flex offers more resistance to air movement through the duct resulting in your fan moving less air. 3) Insulate the duct for less chance of moisture vapor in the duct condensing and pooling in the duct, or running back into the fan housing. 4) It looks like light can be seen coming from the bathroom below. If so, the fan housing installation is poorly sealed to the bathroom below. Seal those gaps/holes, either with canned foam or aluminum tape, etc. Free air movement between conditioned living space and unconditioned space is bad for myriad reasons. See the dark/discolored/dirty fiberglass insulation? That discoloration is usually a result of the fiberglass insulation acting as an air filter. The discoloration is from the fiberglass filtering pollutants put of the air as air flows through the fiberglass. The second fan: Comments remain the same, with one addition. Since the duct is longer, when you replace it with rigid duct, have the duct leave the fan and run it vertical to a height a couple of inches above the height of the gable wall's exhaust boot. Then as it runs horizontal to the exhaust boot, pitch the duct downward a bit. That way if there is any condensation in the duct, it'll run out versus pooling in the duct.