We are not calling this through current 20th century United States legality. Would the people of Jesus’ time see a child emerge from a woman’s womb and consider her the mother?
There are two ways to be a Jew: One is to convert, the other is to be born to a Jewish mother. No doubt that was plenty of evidence, but we keep in mind the scritural narratives that there were reportedly few people available in the Cave/Stable to witness the birth. The authors of Mark and John didn’t seem to think it mattered enough for them to mention.