Blood relatives share ancestors. Everyone else in the family is connected by a legal or personal tie: marriage, partnership, a step link, fostering or adoption. Kinage calls these by affinity when they come through a partner, and names them from the route.
In-laws
Your spouse's parents are your parents-in-law. Their siblings are your brother-in-law and sister-in-law, and so is your sibling's spouse. "Brother-in-law" is stretched further in everyday use to cover your spouse's sibling's husband, which strictly has no name. Kinage describes such routes step by step in plain words rather than inventing a title.
Step relatives
A step-parent is your parent's partner, and a step-sibling is that partner's child by someone else. No ancestor is shared, so no blood link exists. A half-sibling, by contrast, is a blood relative: see full and half relatives.
Adoption and fostering
Adoptive links are legally parent and child, and in most countries the adopted person has the same family standing as a birth child. Kinage names adoptive links in the same way as parent links, and marks that no biological DNA is expected. Foster links are treated like step links: kinship by care, not by descent.
DNA
No shared DNA is expected across a link by marriage, step or foster. The exception is where an in-law is also a blood relative, as when cousins marry. Kinage reports the blood link when it finds one.
Describe a route in the calculator with the partner, step-parent and step-child buttons, or add partners in the tree builder.