For interests sake, does anyone have an explanation for these patterns if they are supposed to be interference,
Interference does not equal random.
What you are seeing is the beating of several very close frequencies affected by lots of things, your body not the least of them. Stop trying to see a pattern, even if you find one then what, it is of no use to you.
Why have you got to use piezo sensors. Why not force sensitive resistors, these are much lower impedance and so will not pick up as much.
Below I've attached what is hopefully my final circuit.
Sorry but that is useless, what communicates circuits to others is schematics. Those are not schematics.