The limit is not Combined like that.

One Family plan and one single plan means you ignore the single and you have one Family limit. The full amount can be put into the Family HSA account, or up to the single limit can go to the other HSA account.

If they both have Family coverage, it's still only the one Family limit, but it can be allocated between the two HSA accounts any way they want to.

They have too much contributed and need to do a corrective distribution.