I think you should totally take the master suite!
Several years ago I planned a trip to New Mexico for myself, DH, my parents, my cousin and her girlfriend, my brother and his girlfriend, and my aunt. We stayed in a 5-bedroom cottage which I found online and booked. When we got to the cottage, DH and I ended up being the last people through the door, and we ended up with a room that was smaller than our closet at home - with no windows, chairs, closet or TV!!!! NO ONE offered to switch with us, even though I was the one who had done all the work. My parents left a day earlier than the rest of us, and when I told my cousin that DH and I were going to move into their room for our final night, she said, "Oh, Katy and I were going to take that room!" She and I never fight (she's my best friend), but I was totally willing to get into it with her at that point if necessary. Fortunately, my aunt stepped in and said DH and I should take the room.
So I say take that room (unless you want to be nice and give it to the parents), and maybe draw straws before you get there so everyone else knows their room assignments ahead of time!