So you have these 24 jacks mounted on a flat ground, you tell the RPi "jack 4: 12cm, jack 5: 16cm ...". RPi sens data to arduino(s). Ardunio should move the jack up/down/stop. You are stuck at the point where the control loop does not work as intenden. If that's about it, drop me a PM.
Using an arduino for every jack isn't something affordable or the path we want to take for this project... at least if I am understanding you correctly. As far as ultrasonic interference, this is the major player in what is slowing down our jacks, and not letting them 0 in on a distance. What are your suggestions around the same price range?