If the husband caught Lewis in bed with his wife, then who put the nightshirt on the dead body before moving it outside.
The second scenario shows Lewis' throat being cut with the gunshots coming after is death. If he was already dead, there would be no blood on his nightshirt. Dead bodies don't bleed.
In the second scenario, Mrs Grinder says her husband is a farmer. But where is the farm? There are no crops, no plowed fields, no livestock other than a few chickens.
The third scenario shows Lewis asking about his 'powders', but in the second he asked about 'powder'. The plural implies medicine - perhaps quinine for Malaria or syphilis, or morphine for drug addiction. The latter implies gunpowder. But he would have no need to ask either since he had already instructed the servants to leave nothing behind.