Yes, the ability of an adult child who is not a dependent but who is on the parents' HDHP policy is a bizarre and unforeseen consequence of the HSA code in Section 223 and the later Affordable Care Act (Obamacare, ACA) which, among other things, changed health insurance so that you could keep your adult children on your policy even when they are no longer your dependents. (The ACA was passed years after the HSA code was passed).
So, yes, daughter can open an HSA and contribute to it until such point as she is no longer on any HDHP policy.
Just to clarify "#2. As long as they are covered on the family qualified HDHP, adult children can contribute the full family HSA amount into their HSA account." should read "into their own HSA." The limits are applied to each HSA.
Actually, the daughter can contribute to the HSA of whichever parent is the owner (HSA belong to the individual, so each parent could have one - BUT the Family limit is shared between them), but the parents must count all contributions to his/her HSA from any source. So in this case, it would make sense for the daughter to make all of her contributions to her own HSA, which has its own limit.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
