Hello. As i understood you have 7 degrees difference between sersors. You use T-IL, that means, you should use thermo-compensating cable. If you use ordinary copper wire you can easily get this diff. Also - what range is used for thermocouples? Any module (and sensor as well) has accuracy +/-0,7% in this case, so on Pt1000 accuracy is exactly 7 degrees. Also regarding accuracy - what integration time is set for these channels?

Anotherapproach - what happends if you switch 2 sensors between modules?