As it becomes virtually impossible for me to assume both sides' roles (i.e. their eventual acceptable yieldings or respective 'red lines' in a negotiation), I've chosen to divide the event into several separate scenes. In each one, both sides explain their starting positions with regard to a particular issue. This is followed by some discussion and eventually a dealing proposal; but I'm not accounting any final agreement, thus leaving open the end.
My ultimate purpose would be accounting such agreement later, after considering readers' comments and reasonings. And I believe such inter-activity would be a nice approach to the real thing. Or, at least, some sort of not-so-usual musing in our hobby. This is why I'd like to encourage you all to drop a thought of your own in each proposed scene --and warmly thank in advance any one's.
[At this my first negotiations round, both sides have agreed a prisoners exchange, regardless of negotiations ultimate result --as a mutul sign of goodwill and eagerness to reach a satisfactory agreement. However, Gallian/French dignitaries are by no means unaware of the strong bonds of Galatans/Catalans toward Emperor Charles, that might get them military involved in adventures contrary to the interest of France. So that they've tried to get reassured about Galatan intentions by means of a similar military alliance to them. Of course, their Galatan counterparts are also willing of some reassurement face to an eventual Hispannic/Spanish rejection of the treaty. How to reach a satisfactory enough agreement?]