Two years ago, I was the only one out of 3 families to get a code. I was able to use the PIN code for our reservation, my parents reservation and my sister's reservation (12 people total). All 3 reservations were 3 separate rooms (booked under a grand gathering at the same resort), 3 different family names and 3 different charge cards. I booked it over the phone with DS sitting right beside me, the CM allowed me to use it with no problem and I was able to use each person's credit card to put down the deposit. He didn't question anything and each family had their own reservation number and received their packets of info at their home address.
That same year - I had a friend who received a PIN code. It was fall break and there were a bunch of us going at the same time. She was able to book another family with her family and they shared the same PIN code. Because it was not a grand gathering or family members - she had to do all the room bookings on her credit card and the other family just paid her back for it. One family stayed at All-Stars and the other family stayed at POR. It was all legit with WDW and the other family was able to check in independently with no problem. I don't know if things have changed but that was all "legal" 2 years ago.