What are his herd conditions like, if he thinks lice are normal? Lice most certainly happen, but aren't the norm. Lice often are most common during fall and winter, though. They like it cool, not hot, so their numbers are lowest in the summer. And shaving really does help, but as you mentioned, it is not an option with this weather. He is spot on that ivermectin pour on works well to treat them. It is kind of like frontline in how it is applied, but a different medication.
You can also use a pyrethrin based horse fly spray. A water based one needs to be reapplied more often than an oil based one. And it needs to be applied enough times to kill the hatching eggs.
As for the bad behavior, you need to start enforcing limits for your goats, now. Start with a simple one, no jumping on humans. Also, no mouths on humans. Start with a simple tool, a squirt bottle each time they try to jump on you or put hair/clothing/whatever in their mouths. Sometimes you need to add a bit of vinegar to the water of the squirt bottle to make it a bit more noxious for them, hit them in the nose or on the ears, never the eyes. A squirt bottle is a kinder method than others out there to discourage them, if they will respond to it ( most goats hate water, some don't care though). My buckling who occasionally jumps up on me gets a (lightly placed) knee to his chest each time he tries. Or I grab his ear (goats bite each other on the ear as part of pecking order, I just grab it, he instantly gets the idea with no pressure). He is still small, but I will not stand for that behavior around any human. But I also reward him when he is being good. He doesn't get them unless he is doing what I want him to do.
Until they are more in line, do not sit down with them. Do not give them any treats unless all four hooves are on the ground and they are being good. Reward good behavior, if they are being quiet around you, give a small treat.
Okay so its similar to training a dog, reprimand bad behavior and give treats when.they are good. When I got.them they were shy but well behaved and then over the winter started jumping on me and eating me. When I go out to feed in the am ill immediately start with positive or negative reinforcement.
I have my dog trained not to jump or bite and it just didnt cross my mind that I could train the goats also.Thank you very much!