Sof Davar, your answer rang especially true to me. Well said.
But IF you must argue with your parents about this subject, you may want to ask a shaila of your LOR, as you need to tread carefully when argueing with your parents, so that You do not mis-step.
I have similar issues with my own parents, and my wife and I simply do not discuss any Torah topics deeper than the superficial with them. And we NEVER EVER engage in comparative religion discussions with them (i.e., when they say their Conservative “rabbi” says…) And if they come to us with questions like the 7 nations, we simply say, “That’s an excellent excellent question, and I’m so glad you asked it. I’d be happy to arrange some time for you to speak with my Rav about it, if it’s troubling you. He knows so much, and you should be talking to an expert. I’m SURE he could answer your questions.”
Here’s some advice that could change your relationship with your parents (as I detect some strain): Always punt when it comes to tough Torah questions with your frei parents. Steer them to a Rav, and let the tough answers come from him – not you!