If you have Vegas Pro, use the multicam feature that was introduced in Pro 8 as it works great.
If you won’t have Pro, then it gets a bit trickier.
My suggestion would be to drop all the tracks on your timeline, one on top of the other.
Use Track Motion to place each camera in one of 4 corners.
With AVCHD footage, your computer will struggle unless you’re running an i7 with a lot of RAM.
Use one track as the master and then start syncing the other tracks to it, one at a time.
Use the track mute options to turn off the other tracks.
Once you get them all synced up, press the “Ignore Event Grouping” icon on the task bar (the shortcut is Ctrl+Shift+U) and delete the unneeded audio tracks.
Disable this option as soon as this is done.
Go through the timeline and drop a marker (shortcut key is m), labeling it as to which camera should be active at this point.
Once you’re done, open up Track Motion on each track and restore it to it’s normal size.
Create a new video track and place it on top.
At each marker, click on the specific track to highlight it, split it using the “s” key and move that event to the top track.
I use the number 8 on the numeric keyboard to do this.
Numeric 2 will move an event down each time it’s pressed.
Once you’re done, mute all tracks except the master video and audio and watch it to see if it’s what you want.
Keep the other tracks there in case you change your mind and want to go with a different shot.