Hamilton Hall's book, "The Back Doctor" is a good reference to learn from. It teaches the basics of managing your back care. I relied on the text for 15 years.
If the muscles are in spasm, get him to an emerg. Get the muscle spasms under control then look at the treatment options. The sciatic nerve is but one of the nerves than can be affected in your lower back. The problem can extend to bladder and kidneys. The severe sciatica can merely be a sign and symptom of far deeper problems. If the legs are moving involuntarily. If there is a bladder or bowel control issue. If he can find no relief in any position. He will need some type of immediate treatment.