In order to get an annual pass with the DVC discount, you have to show your DVC membership card and a photo ID. A guest of a DVC member would not have a valid DVC membership card in their name.
In addition to the above information, you are also required to reside at the same address as the owner of the DVC contract. If you are an adult "child" who lives at the home of a member, then you might qualify.
Unless you are staying with the DVC member on their reservation, you are not entitled to any DVC benefits and perks. If you are staying with them on their DVC reservation, you can pool hop (as long as it isn't blacked out), discounts on dining and rent DVDs from the Community Hall or store for nothing