Marco and Sofia are the children of Carlos, who is Maria's brother. This makes Marco and Sofia Maria's nephew and niece, respectively. Since Robert is married to Maria, Marco and Sofia are Robert's nephew and niece by marriage. In relation to Alex, because Carlos is Alex's maternal uncle (his mother's brother), Marco and Sofia are Alex's first cousins. Marco is not Robert's nephew by blood but by marriage.
Robert and Maria are married and they have one son named Alex. Maria's brother, Carlos, has a son named Marco and a daughter named Sofia. Explain how Marco and Sofia relate to Robert, Maria, and Alex. Is Marco Robert's nephew? Make your response very short.