you file only one 8889 in your return for both HSA accounts since these are both your accounts. be careful with multiple W-2s that one isn't coded as being for your spouse The amounts should appear on each w-2 in box 12 coded with a W. The total of the two amounts should flow to the same 8889-T on line 9
you are correct on what type of coverage to check for each month when you get to the medical expense section the HSA link. To be an eligible month you must be covered by an HDHP on the first day of that month. if you were you're eligible to contribute 8/12 of the full-year $7750. However, because you were covered on 12/1/2023 by a family HDHP under the last-month rule you can make a full year's contribution ($7750) by making up the difference personally by contributing to one of the accounts by 4/15/2024 (7750 less the amount on line 9 of the form assuming you made no other personal contributions). There is a catch, however, to avoid being penalized for excess contributions if you use the last-month rule you must remain covered by a family HDHP for the entire year 2024.
entering the 1099-SA should not have affected your refund assuming the code is 1 in box 3. The form only reports distributions from your HSA not contributions. form 5498-SA reports the contributions. You should get 2 because of the two accounts. the total of these two should match the total on line 9.
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