What should a wife do after discovering that her husband's son (from his ex-wife) has a blood type incompatible with his father's blood type, which raises doubts about his lineage, especially since the son is 12 years old and she is unable to fully veil herself in front of him, taking into consideration the implications of this on lineage and inheritance, and what if she is pregnant with a girl?

If a child is born within the marital bed, he is the husband's son, and paternity is established for him, leading to the obligations of maintenance, inheritance, and the prohibition of marriage due to affinity. His lineage is not denied except through li'an, for the Prophet, peace and blessings be upon him, said: "The child is for the bed, and for the fornicator is the stone." Therefore, this child is your stepson and one of your mahrams, so there is no harm in removing your hijab (definition) in front of him. As for a daughter born to this husband, her father is a father to your daughter, and they are siblings and mahrams to her, as Allah Almighty says: "There is no blame upon them concerning their fathers, or their sons, or their brothers..." (Al-Ahzab: 55). We advise both of you to treat them kindly and raise them well upon faith and good character.