Actually, TurboTax is filling out the Form 8889 properly for a married couple.
From the IRS Publication 969 Health Savings Accounts and Other Tax-Favored Health Plans,
"If either spouse has family HDHP coverage, both spouses are treated as having family HDHP coverage. If each spouse has family coverage under a separate plan, the contribution limit for 2024 is $8,300."
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