Many of the freedom fighters, who you call "remnants of the Somoza regime," are actually former Sandinistas who fled the regime or were forced to flee once it was clear that the promised reforms would give way to totalitarian terror, as we have seen.
This peace plan was not a thumbed nose at either Reagan or the contras. Rather, it was a final ultimatum to Ortega to cease his expansionist designs. Ortega did not choose this path; he was forced upon it. It has not kept him from seeking to manipulate the process to his advantage, though.
Anti-communist sentiment is quite widespread in Latin America. Don't be confused that because Reagan and the five Central American presidents have different tactics that somehow they do not seek the same goal. They most assuredly do. If Latin Americans feel anything negative about the contras, it is not their goals, but their chances for success which they doubt.
It is quite clear what the Sandinistas will do if left alone. They will continue to slaughter dissidents and Miskito Indians. They will continue to suppress free speech and free press. They will continue communist expansion into other Central American countries as they have tried to do in El Salvador. The President knows that the Sandinistas must be stopped. And he is entitled to be wary that the five presidents may drop the ball. Ortega is very crafty.