For the health insurance marketplace, a household is typically defined as the tax filer, spouse, and dependents. Under this definition of household, your spouse has to be someone you are legally married to, and dependents can only be those claimed on your taxes as a tax dependent. When applying for Medicaid you include your spouse and all dependents regardless of whether or not they need health insurance.
Some states provide a slightly different definition of household, so it is important to use this as a guide but to verify with your specific state who is considered part of your household. Additionally, when applying, you will need to provide verification of each household member. Depending on the relationship, verification may include birth certificates, social security cards, a marriage certificate, custody agreements, or another form of identification.
Due to the complex nature of family relationships, there may still be questions whether or not you should count someone as part of your household. Here is a quick guide to help. If you have a specific question regarding whether or not someone is part of your household, you can also contact your county Medicaid office and ask.