Since you wish to incorporate your mac I feel your solution will have to be a hardware/software one. I would not recommend running WoW in a VM; as powerful as the 17" MacBook Pro's are (I have one) from my experience with VMware Fusion and Parallels your performance is going to suffer and could cause sync issues. The last thing you want to do is cut your toon's spell casts short because it was lagging behind the rest. If you can afford it I would recommend you check out Vetra, they have USB keyboard MegaCaster's that will allow you to broadcast one keyboard to multiple computers. This will eliminate the need for cross platform broadcasting software, you just need to deal with it on a system to system basis. Then I would suggest you give each machine it's own mouse for easier control, and use Synergy to help with launching and setup. It's not ideal, but it will work, you just need to think about your setup and try to avoid classes that rely too heavily on mouse targeting as you will have no way to broadcast those clicks. Healing can be done through macro's so that should be easy enough.
I've not had personal experience with the USB MegaCaster's, I personally use a PS/2 setup for my multiboxing, but due to your laptops I think this would be impractical (and you don't want to use PS/2 to USB converters.) Vetra has worked great for me so far.
Just something to think about :)
