Besides having taken a decision to pull the trigger I cannot understand why anyone would wait a good few minutes before pulling the trigger again once someone realised they had not been successful in what they wanted to achieved. Hence, in my opion, and given the general flow of blood from the two wounds, it appears the two wounds were inflicted within a few seconds of each other. Kaldin's explanation, as detailed above, has a logic to it.
--------------------------------
But it does not go any way towards explaining the flow of blood in the opposite direction from the lower wound, which has dried before the blood from the upper wound exits the upper wound. You cannot simply ignore that other flow of dried blood, which came from the lower wound - and which ran in a totally different direction...
in my opinion...
Additionally, you do not appear to take into account for the fact that the bloodied finger-marks around the upper entry wound, have been displaced, and form around the lower entry wound, which can be seen if you look closely enough, and which confirms that the head of the victims was lent forward so that the upper part of the neck / throat, was resting against or upon the lower part of the same?
In addition to these features, there is the large bloodstain on the back of Sheila's nightdress, which was not replicated on the bedroom carpet beneath where her body was photographed by DC Bird (SOC) from 10 am, onward...