Possibly, but if JB wanted to stage a suicide why there and not in the twins' room? If he went to the trouble of staging a suicide by introducing the bible it doesn't make sense to me that he didn't think through the location?
What was SC doing while JB shot NB and June and, if you subscribe to Scipio's theories, fighting with NB in the kitchen?
I am sure Scipio will enlighten me 
Why would Sheila kill herself in there? I have no answer at all why she would. Logic suggests she would do it in the room where she killed her last victim. Kill the last victim then turn the gun on herself if she had decided to commit murder suicide.
Why would Jeremy kill her in there?
1) killing her in her own room might be viewed as evidence someone went in there and killed her the same way they did everyone else then left the gun after killing her.
2) killing her near the kids would make it look like she killed them last. If they were killed last they coudl potentially be considered to inherit property and then their father would get their share.
3) seeing her kids deads could freak her out even more and make her uncoooperative
4) seeing Nevill dead could freak her even out and make her uncooperative
Maybe June was seen as the victim whose body would least freak her out since she liked June the least well out of all the victims
5) Maybe he had not yet killed the twinse at the time he had killed her
6) Maybe he killed the twins already but she didn't know it and he fooled her and told her to cooperate or he would shoot her kids and thus taking her in there would ruin his ruse.
Any of these reaosns could be the answer. You are asking a state of mind question we have to get into the killer's state of mind to figure out the motivation for why he would choose to stage her there.
For all we know it is something even more simple and less thought out and Sheila had woken up, walked into the room to look at her mother then Jeremy came up and chased her to the other side of the room before grabbing her and forcing her on the floor to shoot her.
Since Jeremy never said is detail what happened we will never know he never even gave Julie the full details and only gavee us a glimpse into his state of mind about certain things like thinking a bike would be safer and less chance of being caught on the roads.
What was Sheila doing during the murders?
Well her doctor said that the signs described indicated she was over sedated and would have slept very deeply. So chances are she didn't wake up until Jeremy woke her up to take her into the master bedroom to kill her.
If she did wake up and come out as they were fighting in the kitchen she scould not have missed her mother lying on th efloor so probably would have went and looked, maybe checked on the boys to make sure they were ok. Then Jeremy comes back up and kills her then the boys.
We know that he had ten shots and used 8 on th eboys and 2 on SHeila we don't know if he killed her and then them or he killed them then went and got her to kill her. For all we know he shot 5 times, then 3 into the boys then the gun was empty so that is why 1 was shot less as opposed to making sure he saved 2 to kill Sheila with.