Marcus is the uncle of Sophia and Lucas since they are the children of his sister, Julia. Marcus's unborn child will be the first cousin of Sophia and Lucas when the child is born, as their parents are siblings (Julia and Marcus).

Marcus is not the father of Sophia and Lucas because they are the children of Julia, his sister, and her husband, Alex. Therefore, Alex is the father of Sophia and Lucas, not Marcus. Marcus is related to Sophia and Lucas by being their maternal uncle, as they are his sister's children.
Marcus has a sister Julia, who is married to Alex. Julia and Alex have two children, Sophia and Lucas. Marcus is married to Maria, and Maria is pregnant with their first child. What would be the relationship of Marcus's unborn child with Sophia and Lucas? Also, why is Marcus not the father of Sophia and Lucas? Provide a very brief response.