Since auto insurance is required almost everywhere, it can be a financial burden for people with little money to spare. To minimize the cost, you may want to combine policies with someone else to take advantage of some discounts that insurers offer. This is a common practice in many families, but insurers may place restrictions on who is allowed to appear on your insurance policy.
There are no universal rules regarding who should be listed on your auto insurance policy. Each insurer has its own underwriting guidelines you must follow, so ask your agent what your insurer's expectations are. Generally, insurance companies want to know about and craft your policy to cover everyone who will drive your vehicle on a regular basis. There are a few common ways that insurers define what this means.
Your auto insurance policy will probably contain a definition for the word "household," and offer coverage to everyone in it. At its most basic, this tends to mean all the people living in the same building as you, regardless of their blood relationship. The rationale is that if they live in the place where your vehicle is parked most of the time, they have near-constant access to it and could drive it at any time. Therefore, the insurer wants to charge premiums accordingly.
You may live with young children, or adults of driving age who do not have a license. Depending on your insurer's policies, you may have to list these people on your insurance policy anyway, as excluded drivers. This is because young people grow up, and unlicensed people get licenses, so just because they aren't driving now doesn't mean it will always be that way. If the insurer is aware of them, you can't sneak them onto your coverage without paying the appropriate premiums.
You may want to add someone to your policy who does not live in your home, such as an adult child who has his own residence, or a close family friend. Some insurers will permit you to do this, as long as you're willing to pay the corresponding premiums. There may not be a financial incentive, however, since insurers tend to rate vehicles based on where they are principally parked. If the vehicles are parked in different locations, the discounts from one location may not transfer to the other.