Multiple sensors off one pin
Use an analogue mixer circuit based around an inverting op-amp configuration. The output from the op-amp will be the algebraic sum of all the sensors so if any generate a signal, this will be seen on the op-amp's output. Following the op-amp, a comparator can be used or just feed the input into one of the ADC inputs.

What you have to ask yourself is this: could two sensors receive an impulse in such a way that the combined output signal of both sensors is zero?

If this can happen then you should use a precision rectifier circuit (also based around an op-amp) on each sensor output - then sum them as above. This should mitigate against cancellations as only one half of the impulse-producing waveform will be amplified and no cancellations can occur.