Yes — your spouse and tax dependents qualify even if they are not on your HDHP. This is one of the most underused rules in the code.
Yes. Your HSA covers qualified expenses for:
And here's the part people miss: they don't need to be covered by your HDHP. Your spouse can be on their own employer's PPO and their dental work is still reimbursable from your HSA. HDHP enrollment governs whether you can contribute. It has nothing to do with whose expenses you can pay.
The notable exception is adult children. A child can stay on your health insurance until 26, but HSA eligibility follows tax dependency, not insurance coverage. Once they're no longer your dependent, their expenses stop qualifying — even though they're still on your plan.
Track the patient name on every receipt so a family's records stay untangled decades later.