Hi,
So as i've mentioned on the second comment, unfortunately you cant directly know if there is an inserted simcard in each slot, you can only get to know if the active simcard is present in its slot. But what you can do is change the active simcard, and check again if there is a simcard present, as now the device would check the other slot.
Maybe you could a linux script to make that reads if a simcard is inserted and then change the active simcard and check it again, so this script would generate an report of each SIM Slot, solving your needs. There is commands available for that, should not be that hard.
Best regards.