Trent Reznor is really the only "member" of NIN, as he writes the music, and plays pretty much all the instruments, and of course sings on all the albums. He's had various different musicians for live concerts though.
Nine Inch Nails is Trent Reznor. He had a touring band with him when he played live that changed throughout the years. He occasionally has people help with his studio albums, but Nine Inch Nails is...