Me and my buddy Dave have been doing this for the past year and a half, after two years apiece of solo building. Here's what I've come to realize...
1) IF the two are physically in the same location, this approach works up through building the airframe and wings (empennage, fuse, wings). But it's best to let one lag about a week behind.... otherwise you'll duplicate mistakes (and there will be mistakes)
2) Once the first plane hits the engine/avionics/FWF stage, team up and work to get one flying. The main reason for this is that unless you are strictly following Van's plans/instructions for these items you will be charting new water for your team. The timeline for working out problems will extend beyond the week buffer you have and you will end up getting lost between the two projects.
3) In the end, the time to build them both is not much more than building one - even with the above approach. Once you've "been there, done that" on an identical plane with all problems solved for a given part/section/item, it's easy to repeat with few or no mistakes. For instance, the 'Big Cut' on the canopy took 14 days from start to final shape / sanding on our first one. The second canopy took 2 days.
4) Work out some method to vent differences of opinion. Pick a mutually trusted third party to act as a sounding board, and pre-agree to listen to that advice.
MHO