If all else fails, look and see if you have a lice clinic near you. There's a place near here that professionally removes lice with a heat machine (kinda like a giant hair dryer) that dehydrates the lice, nits, and eggs, they then completely comb through it, use a professional hair treatment and all lice is basically gone within a week and whatever is left (if anything at all), they can easily get rid of.
Good thing he’s a boy and you can cut his hair short enough to get it all out without having to treat it 100 times lol 😂 I remember getting lice when I was little I had long hair and my mom chopped it to my shoulders and still had to treat mine and my sisters hair 100 times but my brothers only took one treatment