Another vote for registering them with your in-laws.
We had an extended family party for my parents 50th anniversary a few years ago and 3 of the 4 families stayed at BCV. I registered the 4 other family members from the one group who stayed off-site within the 3 villas we had reserved (never coming close to the occupancy limit of the 2BRs we had) so we had the keys for everyone since we knew there would be afternoons we wanted to spend together at the pool. Plus, we wanted to be able to have all of the adults have their own keys for access to the rooms for showers, just running around the resort, etc. It worked well, and I don't feel at all like we broky any rules.
We had an extended family party for my parents 50th anniversary a few years ago and 3 of the 4 families stayed at BCV. I registered the 4 other family members from the one group who stayed off-site within the 3 villas we had reserved (never coming close to the occupancy limit of the 2BRs we had) so we had the keys for everyone since we knew there would be afternoons we wanted to spend together at the pool. Plus, we wanted to be able to have all of the adults have their own keys for access to the rooms for showers, just running around the resort, etc. It worked well, and I don't feel at all like we broky any rules.