Too much risk in all this Adam. He wouldn't have known if the adults were awake or asleep, wouldn't know if crispy would bark, or attack him or what he would do, OK, Nevill may have 'fled downstairs' but that would have left the others unprotected because if he was injured he would know JB was in ernest, as for the burn marks find it hard to believe someone would go through all that performance to check if someone was alive. There are much quicker and easier ways than finding an object and heating it up, no .... I don't buy that.
Jeremy thought it worth the risk.
People are usually asleep at 2am.
He knew Crispy. So knows more than anyone alive what the dog would do. If it woke.
June was shot along with Neville. So would have been dead. Neville fled as he was being shot at. Or he followed Jeremy as he went to re load.
No one knows what the burn marks were.