Ok ... so the credit belonged on the 2017 return and only one person claimed 1/2 the expense on their 2017 return and they could not use it up on the 2017 or 2018 return so they now have a carryover to 2019. The other person CANNOT pick up the first person's carryover on the 2019 return.
What the second party needs to do is amend the 2017 return to claim their 1/2 of the cost on their 2017 return then if there is a carry over they MUST amend the 2018 return ... then if there is still some carryover they can carry their own carryover to their own 2019 return.
