Alex is Julie's brother, making him her sibling.

Carl is Jessica's son. Since Jessica is Tom's sister, her children, including Carl, are Tom's nephew and niece, respectively. Therefore, Carl is Tom's nephew. Given that Julie is married to Tom, Carl would be Julie's nephew by marriage but does not have a direct blood relationship to her.

Sarah is also Jessica's daughter, which makes her Tom's niece for the same reasons Carl is Tom's nephew.

Alex and Sarah are not directly related by blood. Since Alex is Julie's brother, and Sarah is Tom's niece (through his sister Jessica), Sarah would be the niece of Julie by marriage. Therefore, by marriage, Sarah could be considered Alex's niece as well, but there is no direct blood relation between them.
Tom is married to Julie, who has one brother named Alex. Tom has a sister named Jessica, who has a son named Carl and a daughter named Sarah. How are Alex and Carl related to Julie? Who are Carl and Sarah in relation to Tom? What is Sarah's relationship to Alex?

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