For the past week, another person peripherally involved in this story, Donna, has been trying to help by having someone that Joe respects talk to him about the situation and see if a compromise can be reached. This person, X, said that he would speak to Joe last week and also wanted to speak to both Joe and Mark. So far this doesn't seem to have happened; Donna has been calling X (or his secretary) every day or so, but so far, as far as Amy, Mark, and Mandy know-- nothing has happened.
Mark spoke to Amy last night and Amy said straight out that she will not force Joe to give up the camera. Mark spoke to Amy again today (I think-- it might have been last night) and said that if X does not speak to Joe by Tuesday, other routes may need to be pursued.
So it seems that Mark and Mandy will be renting a camera again next year at their own expense and Joe and Jessica will be continuing to use Amy and Andrew's camera for an indefinite period, completely expense-free.
More updates as they come along.