Short answer: Usually no. Most plans cover a spouse and your children to age 26. Parents, grandchildren, and other relatives generally cannot be added unless they are your tax dependents and the plan specifically allows it.
Employer and individual health plans define who counts as an eligible dependent, and the standard categories are a legal spouse and your children. Under federal law, children can stay on a parent’s plan until age 26 regardless of marital, student, or financial status.
Parents and grandparents generally cannot be added to your plan; they typically have their own coverage through Medicare or the marketplace. A grandchild or other relative can sometimes be covered, but usually only if the child is your legal dependent or you have legal guardianship and the plan’s rules permit it. Some plans extend coverage to domestic partners, but this varies by employer and state.
Check your specific plan’s definition of an eligible dependent and what documentation is required (such as a birth certificate, court order, or proof of tax dependency). If a relative is not eligible under your plan, help them explore Medicare, Medicaid, or a marketplace plan instead.