In Pensacola Lively One is the best I know of for that many people, I talked to him a couple days ago and he slayed the triggerfish. Out of Orange Beach book one of the resmondos like Sea Hunter, Sea Spray etc. I don't know if they do 20 or not but Sunrise charters out of Destin is AWESOME.
What port, time of year, and type of trip? You may want to go with one of the Headboats if $$$ is an issue. The Resmondo's out of Or. Bch are charging around $4000 a day for 10, with about a 5-10% per person charge over 10.