It would seem highly unlikely that law enforcement would pursue such charges, but never say never. Law enforcement can pursue whatever charges they want.
Clearly the three year affirmative defense would apply in this situation, so I can't imagine the DAs pursuing these charges.
The parents can squawk all they want - the older party has an affirmative defense to prosecution - end of story.
I do not think any charges would arise. Most DAs will not waste their time with what they know is a loser case in light of the defense. It will really depend on the county the prosecutor and how much pull the family has to be honest with you. I could see this happening in some small county but not in a major county. A prosecutor in the Houston area would not accept charges on case with the facts you have presented.
Mr. Tuthill is correct to point out that even though it may be an ethical dilemma for a prosecutor to file these charges if the defendant qualifies for the affirmative defense, they may go ahead and do so. They might stand behind a position like "we have reason to believe the relationship began when she was under 14" (which would make the affirmative defense unavailable for that conduct). Some DAs look at it as their obligation to protect children despite the defense that the legislature has crafted. And yes, whether or not charges are filed would heavily depend on who the victim was, who they knew, and what county this conduct took place in. So they might have a defense against a civil rights claim that they are harassing this defendant with conduct they know to be legal (so long as the belief is in good faith).
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.