Hi, Sharlene -- welcome to the forum!
Each of the military services has its own regulations about flag display and precedence. Fortunately, most of them are pretty much similar. We'll use the Army Regulation (AR 840-10) as an example. Here is what it says about your situation:
"When a number of flags are displayed from staffs set in a line, the flag of the United States will be at the right; that is, to the left of an observer facing the display. However, if no foreign national flags are involved, the flag of the United States may be placed at the center of the line providing it is displayed at a higher level."
According to the same regulation, the order of precedence of the military flags is the way you listed it: Army, Marine Corps, Navy, Air Force, Coast Guard. However, it also says that the state flag comes *before* the service flags.
The bottom line is that your order is correct according to Army regulations, except for the state flag. If your Marine friend wants the US flag in the middle of the line, it should be higher than the other flags.
I hope this helps -- if not, let us know!
Peter Ansoff