YTA. You should apologize to them for taking out your anger on them, when they were not at fault. Even though they weren’t at fault, your nephew apologized to you. The fault lies with your parents who didn’t remember that they had three traumatized kids, not two. It also lies with their father, who abandoned ship. And it lies with the universe because sometimes life sucks. But there wasn’t much two very young kids could have done about any of it. Humans behave in certain ways under stress, and the younger the human, the harder it is to control. It’s up to the adults to figure things out. You need therapy, both individual and with your family. You also need to grow up and take responsibility for your feelings, and not place them on two little boys who did nothing but respond to their mother’s death in a normal way.