Only the account holder can open and hold an HSA — not a spouse, not a dependent, no one else on your plan. Each person needs their own HSA-eligible coverage and eligibility to open one in their own name. (A spouse with their own HSA-eligible coverage can open a separate HSA of their own.) But the funds in your HSA can still be spent on qualified medical expenses for more than just yourself.
You can use your HSA funds to pay for the qualified medical expenses of:
Yourself
Your spouse: regardless of whether you claim them as a dependent
Your tax dependents: people claimed on your tax return
A near-dependent exception: someone who could have been claimed as a dependent, except that they filed a joint return, had gross income at or above the exemption amount, or you (or your spouse, if filing jointly) could be claimed as someone else's dependent.
Covered by your plan ≠ your tax dependent
Being covered under your health plan isn't the same as being your tax dependent. If you have a family member on your plan who isn't claimed as a dependent on your taxes, for example, a non-dependent adult child under 26, you generally can't use your HSA for their expenses, unless the near-dependent exception above applies. (See Rules for HSAs and adult children under 26.)
Source: IRS Publication 969, Health Savings Accounts and Other Tax-Favored Health Plans