Hashirama Senju, the 1st Hokage, married Mito Uzumaki right? So does that make him Naruto's great, great, great grandfather?
Well, both Naruto and Hashirama Senju are reincarnations of Asura. Apart from that, Hashirama could not be Naruto's direct descendant as marrying to Mito Uzumaki does not mean Mito Uzumaki is directly related to Kushina. There might be a slight chance, but the possibilities are endless, assuming the Uzumaki clan is a big clan.
I don't know anything when it comes to user20385's answer since absolutely nothing is known on Minato ' s ancestry as to where his blonde hair came from, but in relation to the actual question, yes Naruto is technically - if distantly - related to Hashirama. No, he's not Naruto ' s great great grandfather (Which would be the line up considering Tsunade is his granddaughter and about 50 years old) as Tsunade and Nawaki are the only two grandchildren known, (though we've no idea if they had cousins) of whom only Tsunade survived to an age to bear children which it doesn't look like she did since Dan died early in one of the Ninja wars.
In the episode "The orange spark" and its following episode explaining Kushina ' s past, Kushina notes that the Senju and Uzumaki clans are distant cousins which is heavily implied to be because the Rikudou Sennin is their common ancestor by some colored art of the manga showing Hagoromo with the Uzumaki ' s famous red hair. (Though I've no idea if these are Kishimoto's renditions or fan made) Whether this is true or not is unexplained.They could just as likely be descended from a second child born to Hagoromo's brother whose story is never explained outside their fight on the Juubi . This would still make them distant cousins regardless of if Homura or Asura is the clan's father.
She also explains she was brought from Uzu to be the next vessel since Mito was up in age and weakening, but it seemed still had a few good years left since she's seen helping Kushina adapt to and prepare for life as a jinchuuriki. We do not know as to where in the clan Kushina or Mito fall in with their births. (i.e. people like to speculate in fanfics that they're both directly born from the head family and as such are equivalent to Uzu royalty) If we were to believe that is the case, then at most it means Mito had a sibling whom had children and one of them gave birth to Kushina, making Mito her great Aunt. That would make Naruto the great great grand nephew to Mito but no closer than that in relation.
In conclusion, Naruto is related to 4 out of the 5 Hokage's in the series. At least as distant cousins as the clan's were very distantly related, and possibly through Mito's marriage to Hashirama Senju as well, though maybe still fairly distantly. Though knowing Naruto, if he knew of this relation and met Hashirama or Tobirama he'd probably still call them both jiji
Perhaps, since they belong to same clan, Naruto could have some resemblance with Mito Uzumaki because of blood line. Considering a scientific fact that DNA structure does contain some memory from its predecessors. You can generally call someone who is old, grand mother or grand father, but it does not mean that they are in relation. Your assumption to say that Hashirama could be great great grandfather is likely a gesture but less likely to be a true relation.
Is Naruto related to Hashirama? Technically everyone is related, how closely related they are depends on how interbred the Uzumaki and Senju Clans were.
Is Hashirama Naruto's grandfather (I think any farther back the timeline goes out of whack)? No, Kushina would have to be his daughter and the flashbacks make this very unlikely.
Naruto is the reincarnation of Hashirama, and Hashirama is the reincarnation of Asura Ōtsutsuki, the creator of the Senju and Uzumaki clans. Basically, Naruto is the reincarnation of Asura Ōtsutsuki who created the Uzumaki clan and the Senju clan, making Hashirama and Naruto Uzumaki from the same clan.
Also, its trait between reincarnations to fight the Uchiha, just like Asura Ōtsutsuki fought his brother who created the Uchiha clan Indra Ōtsutsuki the older son of Hagoromo, making Asura Hagoromo's son as well and grandson of Kaguya. Anyway, the two brothers fought because Indra was possessed by Black Zetsu, and when they died, Asura reincarnated into Hashirama and Indra into Madara who was a friend of Hashirama but then was possessed by Black Zetsu too, forcing them to fight, and then they died.
Hashirama reincarnated into Naruto of the Uzumaki clan which was also created by Asura, and Madara reincarnated into Sasuke. That is why Naruto and Sasuke fight even though Sasuke is not possessed by Black Zetsu, the other son of Kaguya. Anyway, guess that makes Naruto Tsunade's grandpa.
Well, the Sage of Six Paths had two sons, one was Uchiha and the other was Senju. However, the Senju son was also an ancestor to the Uzumaki clan, so if you think hard and research deep, you'll find out that the two clans are related. So the Uzumaki and Senju clans are closely related. So, yes, Naruto is related to Hashirama, as well as Tobirama and Tsunade. Naruto is also related to the Hyuuga clan (the Sage's brother was the ancestor) as well as the Uchiha clan.