"is this correct or can next year calculation be based on family contribution max (even so I am on Medicare?"
Your limit is based on whether you are covered by a family HDHP or a single HDPH. When you go on Medicare, you are ineligible to contribute to the HSA, even if you keep the Marketplace coverage as well.
Your wife's limit is based on whether she is covered by a family HDHP or a single HDPH. She only has to be covered, not be the owner of the policy. She is covered by a family plan at least through August 31, 2023, and then she will either be covered by a single plan (if you drop your coverage when you enroll in Medicare) or she will be covered by a family plan (if you keep your Marketplace family plan even after you go on Medicare.) Her eligibility is not affected if you become ineligible, as long as she is still covered by an eligible plan and is not enrolled in Medicare.
If you do decide the keep the family HDHP Marketplace plan on top of Medicare and it covers your wife after you turn 65, her limits will need to be recalculated. I assumed you would drop your HDHP coverage and switch to a single plan for your wife.
