Laser frequency noise is particularly challenging to mitigate in low Fourier frequency measurement. For differential measurement schemes using heterodyne optical phase-locked loops, this noise can be common-mode suppressed in the final readout while maintaining a flexible frequency offset and a large frequency-shift dynamic range. We demonstrate simultaneous optical phase-locked loops using digital servo systems, with up to 300 MHz offset frequency range, 250 dB open-loop gain at 0.1 Hz, and control timescales suitable for low-frequency measurement. We also detail a four-laser differential measurement intended for use in a precision measurement device that uses optical phase-locked loops, suppressing relative free-running noise to reach below 0.1 H z/H z at 0.1 Hz in the measurement readout.