I am curious as to how one would negotiate a spousal hire in a different discipline. I teach law and my spouse teaches in a medical field.
From what you say, it is not only that you are in different disciplines, but also different colleges. If you school does not have a clear policy regarding spousal hire, then not only the chairs, but also the deans of the two colleges need to agree. If you do not ask for a TT position for your spouse, it would be much easier - but it still depends on how understanding are the two chairs and deans.
I was in this situation some years ago, but both my chair and the other chair were very unfriendly. So I just left.