Loomis has said that they make the decisions by consensus of the HC, Ireland, and Loomis. He said that they have almost always disagreed and when that happens he has to make the final call. He also said that Ireland more or less runs the later rounds, I think 3 to 7.
That being said, I think it's clear that Payton basically got whoever he wanted. I mean he made that clear regarding Mahomes and ever other pick that they made that he gushed about. How if worked with DA, I don't really known, but I suspect even DA mostly got who he wanted.