I haven’t done much MC Redstone in a long time (not in any significant way since some time observers were added). Couldn’t you take the inverse signal for piston 2 and put it in an and gate to piston 1 (or vice versa). Basically make your circuit (p1/2 is piston 1/2) : p1= observer && !p2. p2 = delayed observer.
Edit: Actually, the delay might fuck this up. I don’t know if I can help. It’s been far too long. I don’t have the intuition for it anymore.
I had never heard of mbin. I see it’s a fork of kbin. What does it do differently?