"We are both over 55 so if we both had Single HSA's would the total allowed be $3600x2 = $7200 plus $1000 extra for each of us being over 55, for a total of $9200 allowed? "
Close but not exactly. There is one more trick - while the two spouses are allowed to share the $7,200 any way they like, the $1,000 bonus to the limit belongs only to the owner of the HSA who is 55 and 55+. That is, if you are trying to max out your contributions ($9,200), you can't put more than $8,200 into one HSA, because the bonus $1,000 for the other spouse has to go into the other spouse's HSA. Fortunately, this is not an issue for you because you put more than $1,000 into each HSA.
So it breaks down this way:
$1,000 to your HSA (bonus amount)
$5,100 to your HSA
$1,000 to your spouse's HSA (bonus amount)
$2,600 to your spouse's HSA
The $5,100 and the $2,600 reflect how you shared the Family limit of $7,200; and, as you can see, your amounts are $500 more than the Family limit.
As for how the IRS calculates it, as I have noted, this sharing of the Family annual HSA contribution limit is not obvious, but please read "Rules for married people" in IRS Pub 969. Look especially at the "Example" which follows as it is almost exactly your situation (but only one spouse if 55+ in the example).
Really, TurboTax calculates it the way the IRS wants it. I don't know what you did in 2020, but this is the way TurboTax has done it for years.
@JDS250
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