Since you have an agreement that your parents are going to pay you back, you didn't make a gift, so there is nothing you have to report. It doesn't matter that there is no written loan agreement. Your parents' paying you back is also not a gift, and they do not have to report the repayment. Neither you nor they have to file a gift tax return.
Since there are no gifts to report, there is nothing to split or break down. The gift tax exclusion is not involved.
