How do you deal with super superstitious parents/grandparents? Sometimes, I feel like I'm not a good parent for them just because I don't follow what's accustomed.

Maybe you just have to let it pass, especially with you knowing that they've come from a different generation and they have different understanding of things. If you can, explain what's true and what's not. If they nag, pasok sa kabilang tenga at labas sa kabilang tenga. After all, they still want the best for our kids. It's just that they have different approach when it comes to certain things.