The key to successful negotiation are the two good negotiators who are loyally representing their respective sides. A third party who mediates almost always makes the negotiation go crazy.
In the case of Mindanao, the Muslims have honorable negotiators. The problem is that the government has crazy politically appointed negotiators and some mediators from Mars.
The mediator between negotiators is an unnecessary element in the negotiation. While the middleman is there, the bottom-line objective of negotiation will never materialize. Well, it may, but it will take longer and more expensive than usual. It applies in business. it applies in politics. It applies in war.
Just remove the mediator, let the forces of energy flow, and let the negotiators of both sides realize their respective strengths, weaknesses, opportunities, and threats.
Peace will be achieved when the enthusiasm and sincerity to achieve peace voluntarily comes from both parties, NOT from the mediator.
On the government side, the one and only appropriate negotiator on the Mindanao peace process is The President of the Republic of the Philippines or his authorized representative.