Hi Daniel,
Sorry for the delayed response!
If you use the same master clock on both ADS1282's, it will help keep the ADC's synchronized. However, you will want to start both ADC conversions at the same time. Therefore, you should use the SYNC pin or SYNC command when initializing the device.
From then on, you should only need to re-synchronize the devices after a power-up or wake-up, from power-down mode or standby mode (respectively), because you will need to restart the conversion process.
In applications where synchronization is critical, some customers prefer to apply a continuous clock to the SYNC pin to keep multiple ADS1282 's in a "lock-step" operation. This can correct timing glitches because the ADS1282 will automatically re-synchronize if a glitch (or clock jitter) causes the conversion processes to get knocked out of synchronization.
Note that layout should be considered and trace lengths approximately matched, to reduce the differences in pulse delays to multiple ADC channels on a PCB!
Best Regards,
Chris