Isolating two op amp amplifiers from each other
At the very least, you want to reduce the equivalent resistance of your virtual ground.

You could repalce R14 with a 4.5 V zener or shunt regulator. However this would not track like your current setup if your 9V supply drifts. You might also need to worry about noise and thermal drift if you use a zener.

You could buffer the virtual ground with another op-amp configured as a voltage follower.