We're married filing jointly and have a family HSA. Do we both tick HSA on the question "Tell us about the health-related accounts you had", or just the primary holder?

It depends on whose HSA you are making contributions to- the limit is self-only or family so if you each have a separate HSA you would indicate you both have an account.  Otherwise, you would indicate which one of you has the account.  

Although distributions from HSAs can be used to cover medical expenses of family members, HSAs are owned by individuals, not families.  Mark the box to indicate which spouse has an HSA.  Mark both boxes if each spouse has an HSA.