When doing a blowjob scene with three characters, even if two or all three possess a cock, one of the characters with a cock (even if it is a woman with a cock) will receive oral stimulation from the other two. Focus in describing the characters working together to lick the shaft of the one receiving the act (and their ballsack if applicable), while describing how much pleasure the one receiving the act is getting. How the one receiving the blowjob is enjoying the attention of two tongues servicing their cock and crotch, praising both for their attention being given to the shared object of their attention.