Not only did Julie say one plan Jeremy had was burning WHF down, but he also told Chris Marsden in December 1984 - 'If the house burnt down with everyone inside, everything would be mine.
Was it a good idea ?
Good points :
Well it's less gruesome than shooting everyone in the head.
He could collect on the insurance.
He would not have to ring the police, rounding the suspects to two.
He would not risk having to confront an awake adult inside WHF.
Bad points :
Julies sleeping tablets were not strong enough. Something stronger would require a medical prescription. Which may come back to haunt him.
It was a big house which would have been hard to burn down. Especially from one cigarette.
It was a big house. Surely there were escape routes and attempted escapes. But everyone would have been lying on their beds, having been drugged.
The insurance for the house and items inside may have been low.
It may have been hard to get the insurance money. They may suspect arson.
If the insurance company suspects arson. So would the police. Jeremy would automatically become the main suspect.
He could not insinuate Sheila.
Following on from the random stranger/ burglar threads, it does seem that Bamber's best option was the one he chose.