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 an exemption under Section 152 of the tax code). https://www.irs.gov/pub/irs-drop/n-08-05.pdf.
As long as 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 IRS Publication 969.
Find more HSA-related FAQs here: https://www.optumbank.com/tennessee/customer-support/faqs/hsa-faqs.html.