Wi-Fi sync with all three apple devices?

I have an iPad 2, iPod 4, and iPhone 4. I want all of them to do Wi-Fi sync with my macbook pro. HOw do I do it?

Note: Only the iPod touch seems to work with that, but the other two just won't do it.

Does itunes only allow one device to be set up for Wi-Fi sync?

Help!

Added (1). I have checked all three to sync through Wi-Fi, but only the iPod works.

It depends on the operating system version. If all are high enough you could use iCloud to sync everything.