Forgive, even if you won't forget

I assume that your cousins were children at that time?

I think you have to just live with it peacefully. Smile and just decide to forgive. 

This has happened to a lot more people than you imagined, one way or another. 

People just have to live with it sometimes. And for those who believes in God, it is easier as they can choose to forgive.

forgiving doesn't mean that you forget. Just living with it but focus majority of your time moving forward. This is called human. We are stronger than past hurts and can smile unconditionally. Don't punish yourself or your mother for others' mistakes. Just, no matter how hard it is, FORGIVE. If it helps, go to church. Pray to Jesus. He understands.