#1: He is lucky to have such an awesome brother.
#2 No. The coach is not "the worst ever". But they are incompetent at coaching distance runners, clearly. There are endless numbers of incompetent high school coaches in all sports.
#3 A very similar thing happened to our track team during our senior year many, many years ago. At beginning of senior year T&F season (I was a 800-3200m runner and a team captain) our old (highly-competent) coach changed careers and left and we got a new coach who was a substitute teacher who was a former college sprinter (and a super nice guy) who was 100% clueless regarding distance training. For a couple weeks we grumbled and complained but complied with his idiotic, ignorant back-to-back, short/fast track workouts. We tried to push back, but he took offense and said that we needed to trust him, etc. He said he didn't like us going off campus on roads and trails running mileage and tempos because he couldn't see what we were doing and therefore could not verify that we were actually doing the road/trail workouts. Idiot. (For context, our XC dual meet record was like 12-3 in the prior fall season just 6 months prior with the same squad of 10th - 12th graders!) What a fool. In our case, what I did was I went to the Vice Principal of the High School. This high school vice principal was a former college distance runner and he had been the coach 10 years earlier of one of our graduates who almost made the Olympic team at 880yards. I explained our dilemma. I said that most of us were ready to quit the team (at least I was ready) because of the coach. He said okay and then had a talk with the coach. The next day the coach announced that the distance squad was going to direct their own training with his approval.
So, in summary, perhaps there is a administrator or teacher or athletic director that you can talk to who might understand your bro's situation? And maybe then this teacher/admin can talk to the coach and enlighten them? Good luck, I wish you both the best.