HSA question -> two separate plans...how much can family contribute?

[Swat]

Quick HSA question
Background:
-My wife and son are on a separate health plan than myself through her employer.
-Both her employer and my employer offer high deductible health plan offerings with HSA employer contributions
-We file our tax returns, "married filing jointly."
-I know the 2017 HSA contribution limits are $3400 (solo) and $6750 (family).

Question:
-What is the max we can contribute? Is it still $6750 given that we file jointly? Or can I contribute $3400 to my plan as a solo and she can contribute $6750 to her plan as a family?

[seattlecyclone]

From Publication 969:

Rules for married people.   If either spouse has family HDHP coverage, both spouses are treated as having family HDHP coverage. If each spouse has family coverage under a separate plan, the contribution limit for 2015 is $6,650. You must reduce the limit on contributions, before taking into account any additional contributions, by the amount contributed to both spouses' Archer MSAs. After that reduction, the contribution limit is split equally between the spouses unless you agree on a different division.

The total limit for the two of you is $6,750.

One thing to be aware of for down the road with your son is that if you keep him on your plan until he turns 26, but he's not your tax dependent anymore, he can contribute the full family limit to his own HSA in addition to the family limit you and your wife share.