The catch-up is per individual who is age 55 or over, made to that individual's HSA. Since both you and your wife are over age 55, each of you is eligible for a catch-up contribution to each one's own HSA: 5/12 of $1,000 to your HSA for your 5 months of HSA eligibility and an entire $1,000 of catch-up to your wife's HSA for her full-year eligibility.
$6,621 = 7/12 of $7,100 + 5/12 of $3,550 + $1,000 (rounded to the nearest dollar). That would be your wife's maximum contribution if you didn't allocate any of the family limit to your contribution and you contributed to your HSA only your catch-up of 5/12 of $1,000. $4,725 + $2,479 = $583 + $6,621
