Is the marriage of the questioner to her maternal cousin (her mother's sister's son) legally valid if the questioner is either her husband's paternal niece or his maternal aunt, and how can her lineage be scientifically proven?

You are the granddaughter and not the daughter of the grandfather. Do not pay attention to the whispers of Satan, and seek refuge in Allah from him. Be content with your husband and be happy in your home. Continue reciting the Qur’an, Surat Al-Baqarah, Ayat Al-Kursi, Al-Mu'awwidhat (chapters of refuge), and the morning and evening remembrances to ward off the evil of devils.