To be honest, my opinion would be Genno the Trap Master. Featured in episode 198 of Naruto(original). It describes how Genno's son was the image of Naruto, and how the moment he met नारूटो he stopped his trap on the Leaf Village. My theory is that Genno's son is the 4th hokage.
Neither Minato's nor Kushina's parents are known. So we don't know and it is not Jiraya. Jiraya is not genetically related to Minato या Kushina, as we know so far
In a sense Jiraiya since Minato saw him as a father-figure. Not much was revealed about Minato's family except his own when he gets married and blah blah blah. Jiraiya even thought in an episode of Shippuden that he viewed नारूटो as his grandson.
नारूटो ऐनीमे never showed naruto's grandparents.......
pervy sage is only minato's teacher.......who then became naruto's teacher.....bcz minato entrusted नारूटो to jiraya and gave him the key to open the eight trigram सील, मुहर which is used to open nine tails लोमड़ी, फॉक्स from the cage inside naruto.....he did that in tome of minato's death.......sooo pervy sage decided to train नारूटो to control the nine tail fox's power.........
It's definetly not Jiraya because he is not related from blood to नारूटो या to kushina and Minato. Jiraya was only Minato's sensei. Minato and Kushina's parents are unknown so we really don't know who are Minato's parents and Naruto's grandfather.
So far, there are two जवाब to this. Old man Genno या Jaraiya. Genno's son was लॉस्ट in battle, right? So if Genno's son had been Naruto's father, then he would've been लॉस्ट in battle with the kyūbi! As for Jaraiya, he has some resemblances to नारूटो including a bit of his attitude. He has the will of fighting whether it is या isn't needed. Sometimes he decides to stay out of fighting. But how come we have never heard of Jaraiya's son? He has had so many encounters with women, it's hard to tell! But in my opinion, it's most likely old man Genno. With all the evidence and his son being the spitting image of Naruto, it makes me assume that old man Genno is Naruto's grandfather. After all, why would आप have the same liking for ramen, रामन if आप weren't related? या if आप just really like Ramen...
