Not quite.
The Macrons will have first-person, admissible evidence that Ms. Macron was born female - her own testimony. May also have a birth certificate, documents from the birth of her own children, etc..
What first-person, admissible evidence does Ms. Owen have that isn't true? Absent some kind of affirmative, admissible evidence on her side, I think it is unlikely a judge would conclude that the Macrons have to submit a DNA test to prove something for which there is no reasonable factual dispute.
The Macrons can win the legal war, but lose overall by being tarred with such a dispute. The average adult mind is not as strong as yours. It will continue to believe that Mrs. Macron looks old, dried up, and mannish. Therefore it is likely that Candace is correct. That she was born male.