Family health insurance typically covers everyone in a family, including the insured petitioner and their dependents. This can include the petitioner's spouse and any children or step-children up to a certain age, typically age 26 in the United States. In some states, the law may set a higher maximum age for coverage.
Additionally, other relatives who reside in the same household and who rely on the petitioner for at least half of their financial support may also be included in the plan. This includes relatives such as siblings, half-siblings, cousins, aunts, uncles, parents, or grandparents.
In some cases, domestic partnerships may also be included in a family health insurance plan if the couple is registered as such.
Overall, family health insurance plans are designed to cover any and all family members who are qualified under the insurer's guidelines. It is always wise to double check your insurer's policies to make sure all of your family members are covered.
I hope this helps! If you need more information, this website has some useful resources:
https://www.healthinsurance.org/glossary/family-coverage/