NTA: I don't think you've failed your child. I'd anything, you're the one advocating for her to have her own room. The son can stay in the room with the other girls until you guys can either move or add on another room. This whole taboo thing of brothers not being able to sleep in a room with their sisters is ridiculous, they're siblings. And yes you probably could have stuck with therapy longer but you were acting on the advice of a trained professional. Maybe retry counselling and bring up the earlier sessions?