Complex sentence: The king Louis then decided to negotiate with Queen Catherine and King John III conceding to back down on his demands, while they kept negotiations too with Ferdinand, who intertwined proposals, pressure and menaces with actual movement of troops right on the outer borders of Navarre.
Split into simpler sentences: The king Louis then decided to negotiate with Queen Catherine and King John III conceding to back down on his demands. However, meanwhile they kept negotiations with Ferdinand, who intertwined proposals, pressure and menaces with actual movement of troops right on the outer borders of Navarre.