Its all getting a little OTT isn't it?

A treatment that we've used several times over the years:-

Wash hair. Put on plenty of conditioner - don't rinse it back out yet.

Brush hair to remove tangles. Use nit comb (you'll probably have several from the treatments that you have already tried) to remove as many of the little b*ggers as you can find. Remove any that you find from the nit comb onto a tissue using an old, (disused would be preferable) toothbrush.

Rinse hair.

Repeat until 4 days after you stop finding them.

Job done (as we say in here).

Its tedious but it works.

Have fun.