So the answer is that you CAN write about it. But the question is whether or not you SHOULD. The essay needs to be about you - not about your parents or your family. If you choose to write on this topic, be sure that the point in the essay is what it has meant for you in terms of your upbringing, your world view, and/or how it shapes who you are and what that means in the context of what you offer to a college community.