Parties who find it difficult to communicate often do better with a mediator in the room. Why is this so? I believe people learn to control emotions and anger when a new party arrives on the scene. This might be the "Eddie Haskell effect " (remember "Leave it to Beaver") of trying to impress a third party. More likely it is simply the fact that the interpersonal dynamic changes when a new party enters the fray. Do not underestimate the impact of the mediator's presence. If you are in doubt as to the effectiveness of mediation, give it a try. The potential good far outweighs any down side of expense or the openness of the process.
A mediator need not always be a paid professional. It is always helpful when people are "stuck" to introduce a neutral party to the discussion. This might be a Rav, friend, neighbor, etc. Changing the dynamic in the room often goes a long way to increasing chances for positive dialogue