Changing categories creates tons of graphics issues, from line weights to cut graphics (or not cutting at all). Instead of changing the model category, why not enable the room calculation point in the families? Once that is done I believe that they will report the containing room as any other “room aware” family type would.
See this post for help on enabling that feature
http://dynamobim.org/forums/topic/modify-room-calculation-point-toggle-builtin-parameter/