critique my 8 week half marathon training plan for my brother.

Building to a fast 10-mile run in just a few weeks seems risky. You don't want him to get injured. I'd have the long run just focus on time on his feet at a comfortable pace, and have the only faster run be on Wednesday (or Tuesday if you take my suggestion below). If he can build to 10 easy miles without getting hurt, that should be enough.

I run 5 days a week, and I usually have my longest or fastest runs the days after off days. That way, the recovery runs the following day are more likely to be truly easy. If you have an easy run after an off day, there's too much temptation to do it too fast and then be tired for the more difficult run the next day. You could have him do his long run Saturday and then a short recovery run Sunday, and do his tempo run Tuesday, an easier run Wednesday, and a medium-difficulty run (maybe longer than Tuesday but just as easy) Thursday..

If there are hills on the race course, either make sure that some of his training runs have hills or have a couple of specific hill sessions instead of the midweek tempos.