The GP who first examined Sheila was also Grahame's ( Lugg ) GP who'd said the man's breath always reeked of ale during surgery.
Dr Craig was called to attend the scene under the impression he would be needed to help the police subdue Sheila. When he arrived he had nothing to do other than declare them dead. He spent around fifteen minutes inside the farm house.
Had the chain of communication got the fact of no survivors to him sooner, he would not have attended and the five dead would have been certified/declared dead by a doctor on arrival at the autopsy facility instead.
Dr Craig is of no real significance. His job was to help the police manage difficult people and difficult situations not investigate the aftermath.