1. The child of one's grandparent's stepsibling.
2. The stepchild of one's grandparent's sibling.
3. The child of one's stepgrandparent's sibling.
My step-cousin-pibling is a good person.
Child of their grandparent’s half-sibling with the other grandparent’s full sibling.
My sesqui-first cousin-pibling is a good person.