I just wanted to add that if he's under care of a doctor, he should run any herbal supplements by him/her before taking them. They can interact with any other medications your BIL is on.
I've had bouts of insomnia since I was about 13. It sucks. I'm better now than I was. I have a prescription for pills which are addictive, but I'm not worried about that because I now only get the occasional night or two in a row where I have to medicate, usually every couple of months or so. There was a point, in university, where I would go to bed at 11:30 every night and still be awake at 6am. That was rough!