I know this was a complicated and delicate situation. But I wonder and worry , if the discussions (particularly the one between your husband and son) actually created a forum to discuss why this occurred and how -- or if it was just reprimanding and punitive. Because, most importantly you need to understand if your son actually took the photos, or if he was asked to by someone else (it is after all, a teenagers camera). In addition, has he ever done this with anyone else, or seen photos of this kind, or been asked to pose for something like this by someone else.
As another poster suggested -- creating a neutral discussion in which your children can open up to you about what happened would be the goal. Particularly (since this was a teenagers camera) to make sure that your son was indeed the one taking the photos -- and not the victim of someone convincing him to do it.
i would be particularly interested in finding out what kind of exposure he is having to sexting etc by the teenager living in your home, or her friends. And would try to find out if there are any inappropriate materials,conversations , websites, etc that he has been exposed to . Again , it just seems so odd that it was a teenagers camera that this occurred on -- it makes me wonder what else was on it. Also, that the other family reviewed all the photos in the camera, makes me wonder if they have been having any sexting issues themselves with their daughter. .
This situation brings up a lot of questions -- and I hope that your children will feel they can talk to you about what went on -- and that a dialogue is possible. Your daughter particularly seems to be in a situation now where she is being punished for something she was actually victimized by. She should not be put in a situation where she has to "earn her freedoms back" She should be learning from this situation that your body is private and that you should be strong and say no when someone violates your boundaries or asks you to do something that is wrong.
I worry that they are both being punished instead of fully understood -- and that the motivations and circumstances that surrounded this situation have not been fully investigated.
They are still children, and still learning -- and if they feel they can always talk to you, no matter what the situation -- then everyone will benefit in the long run