Angela is Jack's wife, and Charles is Jill's husband. Jack and Jill are siblings. Therefore, Angela, being Jack's wife, is Charles's sister-in-law, and Charles is Angela's brother-in-law. They are related by marriage, not by blood.

Michael is the son of Jack and Angela, and David is the son of Jill and Charles. Since Jack and Jill are siblings, their children are cousins. So, Michael is David's first cousin, and David is Michael's first cousin.
Jack and Jill are siblings. Jack is married to Angela, and they have a son named Michael. Jill is married to Charles, and they have two children, Sarah and David. How are Angela and Charles related to each other, and how is Michael related to David?
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