So I guess my wife and I will just continue manually uploading our photos to a single Photo library on our Mac. If only there was a family solutions... we just aren't interested in maintaining separate libraries of photos, music, and videos.
Edit: Wait, maybe I'll give jnjbrewer's steps a shot.
----------
Can you just leave the secondary / wife's iCloud account set up on the secondary / wife's iPhone but just disable Photos? Then set up the primary / husband's iCloud account on the secondary / wife's iPhone and only enable Photos: iCloud Photo Library?
It doesn't give you the option to enable photos under that scenario.