How to engage interdisciplinary professors in forming an MS thesis committee and project?
I sometimes have the stinking suspicion that "interdisciplinary" is a codeword for "disorganized, incoherent, or train wreck". What you're encountering is precisely the problem man such programs face, there's no central management of what you are working towards or way to corral the cats into working with you. 

My suggestion is to save the interdisciplinary until you've mastered one discipline. Otherwise, expect more of the same -- having to convince everyone to be on board and losing focus on a current research topic. 

Right now, you're an MS student -- focus on finishing that degree first. If you want to develop research skills outside of that, then take the courses without adding a "minor" to your MS. If after you finish, you want to pursue a PhD that bridges some of the knowledge fields you are working in, make sure that the place you go has a coherent program for bridging them rather than a dream that they can be bridged.