When we added onto our house, the girls also wanted their own rooms. The dividing wall is much the same as you describe and what I did and the girls have loved is: divide the wall into two halves, left and right. Deal with the left side first, perfect that you went with 2X6 as that is what we did. Install shelves between studs. Make a couple shelves taller (for dolls) shorter (for knick knacks) and from floor to ceiling make this half all shelves. Now go into the other room and put a back on these shelves. Top half of this back I made into a bulletin board for the other daughter. Then all you have to do is make an exact copy of shelves on the other side so they don't argue who has more shelves. Actually you can make all of the shelves at once then apply the back according to whose room it belongs to. Each gets shelves for their "collections" and each gets a bulletin board. Worked very well for us.
On another note, for my brother, someone built a set of bunk beds in the center of the room but put a side on one side for the one bunk, a side on the other side for the other bunk so even though they were sleeping in bunk beds, they had some privacy as well as got up in different/individual rooms.
I know you didn't ask for suggestions, just thought I would put them out there for you.
God and family, the rest is icing on the cake.
I'm so far behind, I think I'm in first place.
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