It seems like a million years ago that I left Philly for Marine Corps Recruit Depot, Parris Island. I served from 1987 to 1993. Your brother is about to embark on a life changing adventure. In all honesty...boot camp is not easy...in fact it down right sucks...but it is not without purpose. There will be times when he hates it...and times when he loves it. He will certainly need every ounce of encouragement (in the form of letters) from home. The Drill Instructors at Parris Island are the finest in the world. They will push your brother to limits that he never knew that he could reach. Keep in mind that they will do it professionally and safely. When he is finished and he earns the title of U.S. Marine he will join the ranks of the finest warriors in the world.
During my tour of duty (My basic MOS was Infantry and I was in a Raid Company), I participated in 2 large scale combat operations (Operation Desert Storm...Part I, and Operation Restore Hope, Somalia) and both times, the discipline and stress management techniques I learned at Parris Island kept me alive.
I think that in these troubled times it is important to remember that regardless of what your political views are, or what you think about the war...remember that the kids out there fighting it are our brother, sisters, sons, daughters, husbands, wives, etc. and it is important to support them.
Didn't mean to get off on a rant...Best of luck to your brother, he and all of the other service men and women will be in my prayers.
Semper Fi.