You are 100% correct in your assertion that Sheila was the killer. She killed the other two adults by shooting them, after either one or both had failed in their attempts to disarm her. Whereas the two other adults received gunshot wounds in the course of these events, Sheila did not. The gunshot wounds sustained by the other two adults effectively counteracted any apparent physical advantage they may have had over Sheila (i.e. if it is possible to have a physical advantage over a person going "berserk").
The phone calls issue is very complicated - I'm not 100% on the calls or how to explain them. Unlike you, I do not have a very analytical brain.
That's a good start.
I know Sheila killed the adults by shooting them. She didn't have to fight off both adults. Only Nevill, as June was in bed.
Do you agree with David that Nevill phoned Bamber after Sheila started shooting the twins ? Bit late perhaps. Why did Nevill phone the police 16 minutes later, rather than an ambulance.
Or do you believe that Nevill phoned Bamber before any shooting started ? Bit strange Nevill only said 11 words to Bamber after waiting so long for him to answer, before hanging up ?
Lookout says Nevill heard shots upstairs but thought Sheila was firing warning shots upstairs. Which is why he waited for Bamber to answer.
Either way, what happened in the 16 munutes between Nevill phoning Bamber & then the police ? Feel free to drop Nevill's call to the police, as David & Sherlock did.