RedWeek is a listing website for timeshare owners to post their rental weeks. We have no problem with renting from individual owners. Just note that it's different from the large points managers (like Dave's Vacation Rentals, or Vacation Strategy) who have made a business out of renting out other people timeshare time. You are dealing with individual owners who will vary in their business abilities.
Either way, if renting from anyone other than the resort management, be sure to request written confirmation in your name or the ability to verify on the phone with the resort, prior to making the final payment in full. Verify cancellation policy in writing, as they vary.
We love WBC too. When we cannot stay onsite or at WBC, we have enjoyed the nearby Vistana Resort's Cascades and Lakes sections, and Cypress Point's 2BR or 3BR (smaller rooms there are tiny). Silver Lakes in the Silver Points section is also nice if you'll spend a lot of time at Animal Kingdom, but it's a bit further drive to the other Disney parks, and too far to Sea World/Universal for us.
Others may be recommended but it depends on how much time you'll spend at the resort vs. at the parks and whether you've got golfers and/or children/teens in the group. If your park days are likely to be all-day at the park (not returning midday for a swim/rest break) and you may spend a couple full days enjoying the resort itself, then adding 10-15 minutes to your drive to a full-featured resort is worth it.
Many excellent options... depends on your group.