My brother-in-law is a surgical assistant. Basically he is in charge of the instruments used by the surgeon making certain that the right equipment is available and often hands it to the surgeon. But as far as I know he does not cut.
It’s not easy work. He works a 12 hour shift 4 days a week. This is leading quickly to retirement. :-)
So your BIL is a scub tech. An integral part of the surgical team, and a licensed position.