go to
www.tripadvisor.com and ask this on the Gatlinburg forum.
And I am with Blondie. We vacation in Gatlinburg quite a bit. Cabin rental companies have very specific rules, and a huge house party isn't one of them. Also keep in mind with the giant houses, there is a minimum rental period, often 2-3 days, depending on the time of year. Also.... I have never seen a house that would hold 80 people. 40 or 50, yes, but not 80.
Call one of the many hotels and motels in Gatlinburg, Pigeon Forge and Seiverville, see if they will cater to your group with a block of rooms. Where will you be holding your formal event? You can also ask them about a hotel recommendation.