Since you were on your parents' Marketplace insurance, you have to send the 1095-A and Form 8962. You do not report Form 1095-B.
You can allocate amounts since there are tax returns sharing the 1095-A. If your parents have already filed, there is a good chance they allocated themselves the full 100%. If not, between you decide how to allocate. It can be 33% per person or any way you choose as long as it adds up to 100%.
