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I will try to best answer your question.
I am assuming that your question is how to protect your husband's visitation rights with his son. I would advise buying a response 20 petition to modify custody from Ex based on the fact that the only empirical evidence indicates no sexual abuse (lie detector test results). You should have dna results by now. Delay does not make sense. However, delay does not equal guilt. It is the opposite no dna means no evidence. I would say unless there is evidence there should be no restrictions.
Filing a petition to modify is something you draft. You have to identify the parties. Id the current order in place and attach it and then state the modification you are seeking and why they are in child's best interest. You can get a general template from law library at courthouse.
Lie detector tests can be admissible by stipulation of the parties in civil proceedings.