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.

I'd deal with them the same I deal with everyone and everything else -- respectfully. Superstitions are usually rooted in some truth and just an extreme version of a fact. Perhaps, you can take time to get the elders to explain the superstitions to you. I, too, grew up with plenty of superstitions and I used to mock them. As I grew older, I learnt to appreciate them and while I don't necessarily follow or believe all of them, after understanding their roots, I do find some of them to be useful or true. Those that I think are nonsense, I'd just smile them off whenever someone mentions them to me.