In my view, the scenario of June and Sheila with a gun, or the gun at any stage of the proceedings, fits in well with the idea that there had been tension within the family unit from the evening before. In Ralphs call to Jeremy, he told Jeremy (possibly) that lets say, "she has got the gun", but by the time Ralph speaks to police he is now saying, " my daughter has got hold of one of my guns", which suggests for the possibility that within the space of a couple of minutes both June and Sheila may have had possession of a gun, be it the same gun or a different one...
Police took an interest in at least two other guns from the scene, in addition to the .22 anshuzt rifle, and it comes as no surprise to discover that Sheila's fingerprints were found upon both of these other two weapons, which were a 12 bore shotgun which police retrieved from the gun cupboard in the downstairs office, and a BSA .22 air rifle found upon the spiral staircase which led from the main kitchen on the ground floor to the landing upstairs...
Sheila's fingerprints found upon three different guns within different parts of the farmhouse, namely (a) her prints on the .22 anshuzt rifle found in the main bedroom, (b) her fingerprints found on the BSA .22 rifle which police recovered from the spiral stair which provides access between main kitchen and upstairs landing, and finally, (c) her fingerprints discovered on a 12 bore shotgun recovered from inside the cupboard in the downstairs office...
Seems pretty convincing to me, that at one time or another, Sheila handled one or other of at least three different guns found at the scene after the shootings...
Seems somewhat compelling evidence to suggest that Sheila had handled all of these different type of weapon at some point before she died...