Of course, GSR would 100% be tested and exclude either one from having fired a gun.So forensics will have already determined that it cannot be M/S?
There is no way a family could have staged this.
Also the entry/wound exits wounds, blood spatter etc. will tell them exactly where they would be shot. If they were both prone in bed that's where the blood would be pooling, how it dripped, the blood spatter, and obviously any penetrating shots into the mattress would all confirm this. An investigator would know right away, and forensics would confirm it without a doubt, They know this without the murder weapon present.
To explain further right now it was reported Spence was next to his bed, laying in a pool of blood. If he and Monique were shot in bed there would be clear evidence of the bullet entering at that angle into the mattress, collaborated by blood spatter/pooling, and GSR would exclude them discharging any weapon anytime soon.