"all contractual agreements have been shattered" - I'm not a lawyer but I think that is the key right there. Presumably you have a release form and a music contract, but the son has no contract that states that you have assigned ownership of your intellectual property to him.
If your aim is to regain control of the film, you probably need to engage a lawyer and seek an immediate injunction to prevent distributors from selling the "rogue" film while you pursue negotiations or legal proceedings with the son.
Is the son an integral part of the film? If he tries to withdraw his participation you may also want to seek legal advice about whether you can release your original version on the strength of the existing release forms and music contract.It may become murky if the son/family have invested in the film (prior to the theft). If you raised the funds independently of them you probably have a very clear cut case.
Have you looked into any arts/law organisations that offer legal advice? You should be able to get at least an initial phone consultation with a lawyer free of charge. There are several filmmakers on this forum who are also lawyers, hopefully you will get more responses.
I think these instances are pretty rare, it takes a certain kind of personality to just take something like that! For what it's worth, I am aware of a documentary where the fixer stole all of the exposed film after the shoot and the film was never made. Hopefully your setbacks are only temporary.