My airbag, gauge cluster and seats were recently stolen - I’ve replaced the cluster and seats and just replaced the airbag, however the procedure for resetting the SRS system is only giving me one blink instead of the quick two - and stays on. Both SRS fuses are good.

What else is part of the system? I’ve read that the seatbelt tensioners are but I don’t even know how to test that.

You likely still have an SRS fault if you were doing the reset procedure properly on the SRS diagnostic plug under the dash.

get your car scanned for SRS codes, or you can jumper 2 pins on your obd2 plug and read the flashes to determine the part of your SRS system that is still fubar. Google/YouTube the procedure.