I would suggest that since he is only 7 years older than she, and she was 16 at the time he married her mother (he was 23, and what was the mother thinking?) he was never really a father-figure to her. If not, and probably not, a controlling/guiding/authoritative figure in her life, they should not be charged, since he was not a father to her. Had he been 17 years older, and may have been a father-figure to her, that would be different. That would be my view on the legal situation.
Having sex with your wife's daughter, your step-daughter, just isn't right, whatever the age or relationship. Even if no parental/authoritative relationship really exists, he was still probably taking advantage of his step-daughter.
Over all, leave them alone to seek therapy as needed for their own situations.

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Allan Sherman was classic in my childhood, though we wen't Jewish. His take on many tunes of the 50 and 60 were fantastic! He had no qualms about mocking anyone and everyone!