Thanks.
It does seem awkward to me - why would he choose a position so uncomfortable for him? Sheila sitting there.... She could easily have grabbed the muzzle and turned it away, she had both arms free. I have a hard time buying that she would just sit there taking it!
Implausible, I have to say, I have the hardest time picturing this!
But OK, please, if you would describe what you think happened after the first shot. Again, minus slurs. 
P.S. I agree that she probably sat on the bed for the first shot, but I think she shot herself. There seems to be an indentation in the duvet (to the right in the picture) where someone sat.
First of all since he wanted it to appear suicide he could not fire from too far away or the whole plot would be spoiled. If a gun is fired too far away for a victim to have held it then it is not suicide. SO the gun had to be held at a distance which she coudl grab the gun if she wanted to try.
Second, shooting from the hip is not uncomfortable.
Shooting sitting would not necesarily be uncomfortable either but would have the disadvantage of Sheila potentially spoiling the shot.
The advantage of standing is that you can have very good control over the weapon so that even if she tries to push the barrel away you can prevent her from doing so because you have more leverage than she does since she is seated on the floor while you are standing. That is why you pick that position.
Seating her on the bed would be no good. Her neck would be too high for you to shoot from the hip you would have to hold the gun higher. If she falls backwards you miss. You want her against something so she can't move. She would have fallen backwards after he shot her if she had been on the bed so would not have bled down her arm and in her lap.
She was on the floor against something. She didn't blled much, that indicated the second shot was not fired very long after the first. If there were a long gap much more blood would have been on her arms/dress. But her heart stopped not too long after the first shot. The second shot is why.
So he shot her, he saw she was still breathing so he shot her again. Since he wanted to lay the gun on her body to make it appear she fell flat he pulled her body away form wherever she was propped.
This left the tell tale marks that she had at one point been sitting up though and spoiled the efforts of trying to make it appear she was in the middle of the floor when shot and fell flat.
This was a mistake, he over thought it and wanted to stick the gun on her instead of leaving it in front of her.
Then he made another mistake by trying to make it appear she had read the bible.
Of course shooting her with the suppressor attached was yet another mistake. Obviously it was after that he figured out it was too long for her to have shot herself with so he removed it. Instead of sticking in near her body he decided to pretend it wasn't used at all and made up the tale about the gun being left out in the kitchen sans suppressor.
The more you involve yourself and make up complicated tales though the more problems that can arise. That is why lawyers want clients to not speak at all. That prevents them from saying something that could bite them in the ass later. To try to hed off the proverbial tangled web.
"Sheila fired all guns in the house, she went shooting with me, I left the gun on the kitchen table."
"Sheila didn't fire any guns with me I never saw her fire a gun. She was next to me in the kitchen though as I loaded the magazine so she saw how to load the bullets in. I left the gun on the settle. No I had not used the gun a week prior to the murders"
Jeremy he last known user of the gun says it was in the closet with the scope and suppressor attached what do you have to say about that. "I used the gun multiple times during the week leading up to the murders and it sometimes had the scope and suppressor attached but other times didn't so he wasn't the last known user like you think"
When you make statements and then keep changing and contradicting them as more information comes in from others then you have problems. If you had just shut up then these problems would not exist.
