There is no harm in one person getting fast passes for multiple people. In reality it helps speed up the process. I have no less that 5 tickets in hand when I get fast passes. I got behind a large tour group of 30+ people last week each with one ticket in hand and it made complete chaos of the Soarin fast pass line.
A couple suggestions for "good FastPass ettiquette" I would consider if you're getting 15+ FastPasses at one time:
-For really large groups, perhaps have multiple people go and get FastPasses and split the tickets up so that each person isn't getting more than 15-20.
-Choose an out-of-the-way machine. Not always a possibility, but at some locations there are "more convenient" machines that are closer to the main walkway. Space Mountain comes to mind where the machines closer to the central plaza are busier than the ones near the actual entrance.
-If there's a line for all machines, try and warn anyone who gets in line behind you of what you plan to do so that they can make an informed decision as to whether to stay in that line or switch to another machine. It's the same prinicple as a supermarket checkout. If there's two lines open and one has a cartload of stuff and one only has a couple items, a person would prefer to get behind the couple items. You are that shopping cart loaded with stuff. At the FP machines, people don't have the same visual cues about which transactions will take longer, and assume that everyone has one item.
-When you finish, give a quick "Sorry about that" to anyone who's been held up behind you.
-Lastly, as you leave, check the time on the LAST FastPass that you got and use that to plan your return time. There's a good chance with large groups that the FP time will change between the time the first and last ones are printed. If you return at the very beginning of the first FP's window, you may find yourself with part of the group not being able to enter. So to make both the CM's life and yours easier at FastPass Return, come back *after* the latest FP time in your group.
-Rob