Yes, you can connect extractor ducting together to avoid multiple vents. But do not use one of the T connectors, make sure it's a Y connector with the angles very steep, otherwise you will be pumping from one room and some vapour will work it's way into another room. You can fit back draught shutters within the ducting though to help with that. I used this here, and didn't need those -
That has nice steep angles, so for extracted air to return to another fan, it would have to double back on itself. It won't do that, it will take the easiest route instead, which is straight on. You could connect a couple in sequence I guess for your three fans.
You can buy it from here -
http://www.diytools.co.uk/diy/Main/sp-1-979-32537-record-y-connector.asp
I didn't need condensation traps either, just make sure the fan overrun timer (if it has one) is on long enough to clear any vapour away completely.
It might be easier extracting through the roof, it was with me. In a lot of cases you can just buy a concealed tile vent, the same size as your existing tiles, so it's just a case of slipping a tile off, and replacing with the vented one. Make sure there's no timber behind the tile you take off though, as you'll need to cut a hole in the felt to take the ducting which connects to the underside of the tile. You might be able to reach a suitable tile from the ladders, if there is one you can remove close to the edge, and avoid having to climb on the roof.