Hi Michele,
How fun to plan a getaway with some long-distance friends - a Disney Cruise is the perfect place for a reunion! I have sailed with family that had booked their own vacations, and it was very simple to have our reservations linked together. I suggest that both parties call (800) 951-3532 and ask to have a link to the other reservation (it will help if you swap reservation numbers). They will simply link the reservations and put a "traveling with" note on each of your files.
As for the room location - once the first reservation is made, simply have the other party indicate that, again, they are traveling with "familyname" in stateroom "#" and would like a stateroom nearby. You could actually look this up online at
www.disneycruise.com to get and idea of what part of the ship you would like and see how many cabins are available in that area. Simply start the booking process and when given the option to "select your stateroom" select it to see the available cabins.
I think the last time I traveled with a large party we had linked three reservations, and had 11 people total. We were seated at one table together, it was wonderful!
This sounds like a lot of fun to plan - be sure to come back with all your questions!