An HSA is never a joint account. The law dictates that an HSA is owned by only one individual, not jointly, even though distributions from the HSA can be used to pay the medical expenses of that individual and that individual's spouse and dependents. If your HDHP insurance covers both you and your spouse, or covers you and another family member and the spouse has separate HDHP coverage, you and your spouse can split the family contribution limit between the two of you and each can make separate contributions to each individual's own HSA account.
An HSA deduction can affect the amount of the self-employed health insurance deduction when the insurance is purchased through the marketplace and is eligible for Premium Tax Credit calculated on Form 8962. This is because the PTC calculation depends on AGI and AGI depends on the deductions for the HSA contribution (as well as on the deduction for the self-employed health insurance deduction in an iterative calculation).
