Thank you @dmertz.
To confirm my understanding, it does not matter who is the primary on the HDHP - eligible individuals under that HDHP can contribute to an HSA as long as the total contribution for the family attached to that HDHP does not exceed the annual limit.
Couple of follow up questions -
Are there other limitations for this (like in IRAs contributions cannot exceed earned income etc.)
Will I need additional paperwork if I allocate to multiple HSAs?
Again, thank you for the help.
