You are correct that in this case the self-only limit applies to each spouse separately. TurboTax handles this properly. TurboTax will prepare your tax return will include two Forms 8889, one for each of you, each entirely separate from the other. In the HSA section of TurboTax, make sure that you indicate self-only coverage for each, not family coverage.
Each spouse's contributions must be made to that spouse's own HSA.
You can test the scenario in 2024 TurboTax by entering amounts equal to the 2024 self-only limit. (You can also test using the 2025 limits, but that requires doing overrides in forms mode of the download version of TurboTax.)
