Because they were crapping themselves. The didn't know every one was dead.
Best not to knock over stools, sugar bowls, smash crockery and ceiling lights then.
Why would they be scared ? They were experienced, padded up and with guns.
Anyway the evidence shows there was a massive kitchen fight between Neville and Bamber. This was straight after Bamber had unloaded all bullets in his opening salvo upstairs.
Unless someone can tell me when the kitchen fight between Sheila and Neville occurred.