If you could have periodic joint meetings with your "Fab Four" exec. board and just take the time to socialize with each other i honestly believe that your good relationship with each other will "trickle down / spread out" to the rest of your band(s) and music department. Then you will have each other AND the other bandsmen / musicians to call on when you do these great projects!
I have seen some campuses where TBS / KKPsi / Sigma Alpha Iota / Phi Mu Alpha just don't do the "working together" thing and i can't for the life of me figure out why. i WISH we had other like-minded organizations on the yard when i was in school... but i digress.
I agree that the best way to work together is to COMMUNICATE with each other. I mean, music
is universal so i imagine we already speak each other's language.