All the details are in publication 969.
https://www.irs.gov/forms-pubs/about-publication-969
If you are covered by a non-HDHP, you can't make contributions to an HSA, even if you are also covered by an HDHP.
If your spouse's only coverage under this scheme is a family HDHP, then they can contribute to an HSA. What counts is how they are personally covered, your coverage doesn't affect their contribution eligibility. However, if your spouse also had reciprocal (secondary) coverage from your plan, they would disqualified from all HSA contributions.
If your spouse is covered by an eligible family HDHP as of December 1, 2024, and plans to be covered for all of 2025, then their contribution limit for 2024 is $8300, and their contribution limit for 2025 is $8550 (this is using the last month rule for 2024). However, assuming you can't make the change that soon, and your spouse has single HDHP coverage for 2024 with the family coverage starting in 2025, their limit is $4150 for 2024, but will still be $8550 for 2025, as long as they are covered under a family plan. If your spouse is age 55 or older, they get an additional $1000 catch-up contribution added to either limit.
