I note that one was required for immediate and one for standby. This suggests that they knew persons were possibly alive and in need of treatment, otherwise both would be required to standby prior to police entry to the premises. So it is possible that June or Sheila did use the phone. I hope you would agree it would be unlikely that Nevill or the twins used the phone. If it was Sheila, given her wounds found on entry, it is unlikely she would need immediate treatment. This suggests it was other persons who were in need of treatment. I suggest it was June. If Sheila announced her intention to commit suicide it would have triggered and earlier entry to the premises.