When you mention large groups, someone always suggests renting DVC points...but as someone that often travels with other couples or family groups (and who is usually the one who does the planning!) I can tell you that for a variety of excellent reasons (health, family issues, job, etc) the reality is that people sometimes need to cancel. The larger the group, the better the odds someone will have to drop out.
Renting DVC points is a risk as you could lose money if people cancel out and you are either left with a larger unit than you really need or extra units. For a group You need flexibility--my recommendation would be to do individual resort rooms for each couple or famly, paid for separately (room only reservation). This way if someone needs to cancel, no problem.
Gooc luck!