Your situation is quite similar to mine. I take pride in the effort that I exert toward being prepared to make a good shot when the time comes. My dad and brother are very similar to your brother that shoots poorly because of lack of preparation. They shoot a few times before the hunt and then call it good, regardless of where their arrows are hitting the target. Thankfully my dad doesn't do much hunting. My brother does a fair share though, and by my standard has no business drawing on a deer. I've tried to coach him a little but he never puts the time in to become even remotely consistent. The best thing I can do at this point is tell him to limit hos range to 15 yards. Perhaps if you make that same suggestion and are willing to do the same (lead by example) your brother will be less likely to wound, regardless of his ability.

Good luck.