I'm guessing dual relationships in parents/siblings would act similiar to dual romantic relationships. A sense of respect and ignoring each other so you can find yourself, but then deep love and intensity when you really need it the most. Not manipulating your "weaknesses" against you like most people would do, and not trying to change who you are. Not overidealizing either like your contrary would do, but true acceptance. "Real, practical love" as good as it's gonna get. "Wow, you gave me just what I needed, I didn't know what I needed, but I see the light now and you gave me it- and now I can actually progress."