If you ask me I would say ten Haag would start Mount slowly into the matches and then perhaps as a winger later on as matches go by. I don't think that it will be two CAM's as it would really bring back United to their old form and has to cover a lot of ground in opponent counter-attacks. It would be really risky. Two DM's is fine as it is in my opinion.
Ten Hag can use two defensive midfielders in a game, but only if he feels the opposing team can dominate the midfield to build up the attack. He could apply that idea to the derby against Manchester City but if the opponent is a different team then I think one defensive midfielder is enough.
Playing two defensive midfielders is a defensive style, sometimes not very good, especially when you are a few goals behind your opponent. Such a strategy is good only if the defensive midfielder can play in two different positions and has good flexibility in adjustments.