You can use your HSA to pay for eligible health care, dental and vision expenses for yourself, your spouse or eligible tax dependents (children, siblings, parents and others who are considered a tax dependent under Section 152 of the tax code). https://www.irs.gov/pub/irs-drop/n-08-05.pdf.
If the person is in one of the above categories, you can reimburse yourself for the cost of their qualified medical expenses with tax-free money from your HSA. It doesn't matter whether the person was covered under your CDHP or even whether they had health coverage at all. For more detailed information, please review the current edition of IRS Publication 969 or contact your legal or tax advisor.