4 timers
Let me see if I've got this straight. You're running four of these circuits off of the same switch (S1)? and you have all of the reset pins (pin 4) tied together? If so, it's no surprise you get the same number on all 4 displays fairly often. It's the same circuit getting triggered at the same time, with the only "randomness" being in the tolerance of the timing components.
If this is the case, there's no frequency "leeching" going on between timers, your original post sounded a little suscpicious. Two things would help:
1) Increase the oscillator frequency to about 10Khz or greater. With the components shown, the timer outputs a 48Hz clock. The higher the frequency, the more random the result will be when releasing the switch. Of course, there's a point of diminishing returns.
F_osc = 1.44 / [(R1 + 2R2) x C1]
2) Vary the values of the timing components in each circuit. For example, run the timers at 8, 10, 12, and 14Khz.