Your plan:

[Adam]

That is an option. Go straight into the main bedroom with the intention of discharging all 11 bullets.

That would almost certainly negate June & Nevill.

The 11 shot massacre is no longer possible. But even with 39 years of hindsight, that would be extremely hard to achieve.

Bamber went into the main bedroom with 9 bullets, probably intending to fire 8.  As said he needs to be given leeway. There are good reasons why he did this.   

[Adam]

Going for a multiple shot massacre straight away gives you the advantage of being able to kill everyone quickly. No waiting for someone to die from 1 or 4 shots. 

The exception is Sheila. He could only shoot her once. Then wait and hope, for a limited time.

[Adam]

If you may have to wait for Sheila, you might as well attempt an 11 shot massacre and simultaneously wait for other people that have not died instantly.

You can always revert to a multiple shot massacre if things go pear shaped mid massacre or people take too long to die.

[Steve_uk]

I think I would have went into the main bedroom and put on the light,then stood by the door and aimed for their heads,shooting the first one to sit up,then the other.
Thats what I would have done,put on the light and then aimed the rifle in ready,shooting who sat up first before they knew what was happening.
Obviously if Sheila nor the boys stirred with the noise,the boys would have been next.
I have absolutely no idea how or where to kill Sheila and make it appear like suicide.
Thats the best I can come up with,although obviously Nevill wasn't shot dead as he sat up in bed.Why?

There was only blood on one side of the bed, wasn't there? I doubt both Nevill and June were behind the covers at the time of the first shots in the master bedroom.

[Adam]

There are advantages and disadvantages of attempting a multiple or an 11 shot massacre from the outset.

The evidence is Bamber attempted an 11 shot massacre & changed to a multiple shot massacre when that failed.   

[Adam]

There was only blood on one side of the bed, wasn't there? I doubt both Nevill and June were behind the covers at the time of the first shots in the master bedroom.

Where else would Nevill be?

How did Bamber manage 2 face shots from inches away?

[Steve_uk]

Where else would Nevill be?

How did Bamber manage 2 face shots from inches away?

Nobody really knows. He might have got up out of bed at the instigation of June.

[Adam]

Nobody really knows. He might have got up out of bed at the instigation of June.

Well the bullet casings are in the bedroom.

Do you not think June & Nevill would be sleeping? They were upstairs behind closed doors at around 2am.

[Rob_]

I would also go for an 11 shot massacre. However I would enter the main bedroom first. Sheila had to be shot last. I believe the twins would remain sleeping. The rifle had a silencer.

I would allocate 8 bullets equally into June & Nevill.

This would be done from June's side of the bed. To avoid any possible physical confrontation with Nevill. The rifle with silencer was long enough to reach across the bed.

Nevill would be shot 4 times before June.

My plan would be to only fire 11 bullets/the 3 remaining bullets into Nevill if he managed to get out of bed. I would want to avoid a physical confrontation.

If 11 bullets instead of 8 had to be fired in the main bedroom, it would then have to be plan B - a multiple shot massacre.

Why does the rifle have to be long enough to reach across the bed? Are you saying Sheila had to get very close or that Bamber was a very bad shot?

[snow66!]

Speed would have been of the utmost importance in JBs mind I believe so that Sheila could be dealt with before she was aware of what was going on.
So,sneak upstairs and put on the main bedroom light,stand by the door and aim the rifle at Nev/June and wait till they sat up,then one shot each between the eyes.Nip dwn the corridor and into the twins room,again one head shot each then back out to corridor to see if Sheila had roused with the noise.The quicker Nev/June,twins dealt with the less chance Sheila had to get up and cause any hassle or run downstairs.
Again,how I would have managed to kill Sheila without causing her bruises I do not know.
Anyway,this is not how the killing unfolded,for some reason both Nev and June received seversl body shots for some reason to begin with,and aloud to roam about,struggle and cause mayhem for the killer before receiving head shots to finish them off.Very strange plan,why didn't the killer at least manage to kill one of the adult victims with a single head shot before they knew what was going on?
Well,QC always argued that all the mayhem and the struggle in the kitchen points to Sheila as the killer, and I agree.If JB was the killer Nevill and June would have been shot between the eyes and stopped in their tracks before they even knew what hit them.

[Adam]

Why does the rifle have to be long enough to reach across the bed? Are you saying Sheila had to get very close or that Bamber was a very bad shot?

The rifle with silencer attached was long enough to shoot Nevill from close range from June's side of the bed.

[Adam]

Speed would have been of the utmost importance in JBs mind I believe so that Sheila could be dealt with before she was aware of what was going on.
So,sneak upstairs and put on the main bedroom light,stand by the door and aim the rifle at Nev/June and wait till they sat up,then one shot each between the eyes.Nip dwn the corridor and into the twins room,again one head shot each then back out to corridor to see if Sheila had roused with the noise.The quicker Nev/June,twins dealt with the less chance Sheila had to get up and cause any hassle or run downstairs.
Again,how I would have managed to kill Sheila without causing her bruises I do not know.
Anyway,this is not how the killing unfolded,for some reason both Nev and June received seversl body shots for some reason to begin with,and aloud to roam about,struggle and cause mayhem for the killer before receiving head shots to finish them off.Very strange plan,why didn't the killer at least manage to kill one of the adult victims with a single head shot before they knew what was going on?
Well,QC always argued that all the mayhem and the struggle in the kitchen points to Sheila as the killer, and I agree.If JB was the killer Nevill and June would have been shot between the eyes and stopped in their tracks before they even knew what hit them.

Nevill was shot twice in the face from close range.

June was shot in the neck and chest from close range.

The pathologist suggests June's arm and leg shots were when she was defending herself. This would have been at the same time Nevill started reacting.

[Adam]

As said Bamber has to be given some leeway.

It was a first time massacre attempt with a rifle for shooting rabbits.

But appreciate June & Nevill briefly surviving a 9 shot attack will result in supporters automatically saying it points to Sheila.

[snow66!]

Nevill was shot twice in the face from close range.

June was shot in the neck and chest from close range.

The pathologist suggests June's arm and leg shots were when she was defending herself. This would have been at the same time Nevill started reacting.

But why didn't JB just take aim and shoot Nev/June square between the eyes Adam?

[snow66!]

As said Bamber has to be given some leeway.

It was a first time massacre attempt with a rifle for shooting rabbits.

But appreciate June & Nevill briefly surviving a 9 shot attack will result in supporters automatically saying it points to Sheila.

But it does point to Sheila Adam,give JB a bit of leeway if you wish,but to allow both Nev/June to get out of bed as you claim,impossible!