Immediate family members refer to your parents, grandparents, brothers and sisters with the same father/mother.
Collateral relatives refer to the immediate family members of your parents, grandparents and grandparents and their immediate family members. That is, your uncle, aunt, uncle, menstruation and their parents and children.
Your uncle's children are collateral relatives. Therefore, you can't apply. The political review will mention this information later. If it is found out after registration, it will be regarded as cheating, and it will not be recorded but it will lose the qualification for this exam.