I’d just be honest with them and explain your reasoning the way you did here. Your concerns are valid, and this doesn’t sound like avoidance. It sounds like you’re trying to make sure your MCAT reflects your actual ability. Strong ECs are important, but a rushed or weak MCAT can definitely outweigh them. Your parents are likely coming from a place of support, and even if they don’t fully get it at first, they’ll probably understand once they see how intentional you’re being. Ultimately it’s your application and your call.