Melted coil packs

Hi, my brother has the car listed above. He just changed the coil packs and spark plugs six months ago. Yesterday he had misfires in the plugs. The coil packs were melted and one the spark plugs one was burnt and there was one that had oil on the spark plug. What could cause this? I read it could be from the valve covers are leaking. Is there anything else that could cause the coil packs to burn up and also cause the spark plugs to burn up and have oil on them?