No, they are not related. Tanjiro, by PURE COINCIDENCE, heavily resembles Yoriichi Tsugikuni, the creator of Breath swordsmanship, the only other person to use Sun Breathing, and the only person Muzan ever feared.
Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that compliments his position as Upper Rank One.
There is no direct relationship between Kokushibou and Tanjiro. Namely, Tanjiro couldn't have met Kokushibou since Kokushibou is much older than Tanjiro, and there is no direct family relationship between them.
Kokushibo (黑死牟) is the secondary antagonist of the manga/anime series Demon Slayer: Kimetsu no Yaiba. He is Upper Rank One of the Twelve Kizuki, and the archenemy of his younger twin brother, Yoriichi Tsugikuni.
However, Tanjiro is not a descendant of Yoriichi Tsukiguni. Tanjiro is the descendant of someone who knew Yoriichi personally and was a good friend of his as well. Sumiyoshi was rescued by Yoriichi when a demon threatened his life. Since then Yoriichi often met him and they became close acquaintances.
But if we are talking about the human form, then it's a big fat NO, because Tanjiro has just mastered the Sun Breathing whereas Yoriichi is the inventor of it, also he's way more powerful and holds an unfathomable battle intellect, larger than any Demon Slayer in history, so in conclusion, no one is remotely close to ...
It appears to be nothing more than a simple coincidence that the Kamado men have the same auburn hair as Yoriichi, and the Hanafuda Earrings they've passed down that Tanjiro now wears are the very pair once worn by Yoriichi himself.
Tanjuro Kamado ( 竈門 かまど 炭 たん 十 じゅう 郎 ろう , Kamado Tanjūrō?) was the husband of Kie Kamado and the father of Tanjiro Kamado, Nezuko Kamado, Takeo Kamado, Hanako Kamado, Shigeru Kamado, and Rokuta Kamado.
Yoriichi was incredibly proficient in his Sun Breathing, being able to take down demons effortlessly and even overwhelm the Demon King and strongest Upper Rank.
However, wonder soon gives way to rage as Kokushibo's head is cut off, and, to the horror of the four Demon Slayers, Kokushibo regrows his head.
It was Yoriichi's sword, he found it inside Yoriichi Type Zero doll when he destroy the head. And then hotaru took the sword to fix it. Tanjiro also use Kyojuro's tsuba in this sword.
Yori give his earrings to sumiyoshi (tanjiro's ancestor) because he's the only yoriichi's friend and he trust him the most, and sumiyoshi promise him if he will pass down the hanafuda earrings and the sun breathing (or hinokami kagura).
Tanjuro Kamado was the name of Tanjiro Kamado's father. He passed away before the event of the main story of the Demon Slayer. It is not mentioned how long Tanjuro had passed before the story, but in several flashback scenes, we can see him interacting with a younger Tanjiro.
That being said, Tanjiro's rank is unknown, and his rank was last revealed in the Entertainment District arc. In that arc, they were at Kanoe, which is fourth from the bottom. Since Kiriya Ubuyashiki announced the disbanding of the organization, Tanjiro doesn't get the chance to become a Hashira.
Zenitsu blitzing Upper Rank Six, Kaigaku. Immense Speed & Reflexes: Zenitsu is extremely fast, being able to easily move faster than even the eye can see.
Sakonji Urokodaki is one of the playable characters in Demon Slayer: The Hinokami Chronicles. A former member of the Demon Slayer Corps, Urokodaki is Tanjiro's master and he was also the master of Sabito and Makomo before they died.
Curse of Kibutsuji
The curse prevents Muzan's name from being spoken aloud, and any who do will meet a horrible demise. One demon, Susamaru, faced this reality when battling Tamayo. Susamaru accidentally shot Muzan's name aloud, attempting to defend his honor with her mind clouded.
The explosion, which was enhanced by spike traps, manages to injure Muzan. Before he is able to regenerate fully, Tamayo appears and uses her Blood Demon Art to keep him in place, while using a drug that can turn him into human. Using this opportunity, Gyomei Himejima appears and destroys Muzan's head.
Technically, the elder of the two Sakuras` was actually Muzan`s child, by way of his mistress (Lady Jade Wong), who had one of her eggs inserted into Anne`s body.
Even 400 years later, Muzan's fear of Yoriichi remained fully intact, as simply laying eyes on Tanjiro's hanafuda earrings caused him to recall their clash.
Tanjiro certainly did a lot of good with his Water Breathing techniques, but his ability to use Sun Breathing both gives him an edge in battle and allows him to stand out among the incredibly powerful Hashira he fights alongside.
Kanata is a young man of reasonable height with short black hair, cut into a neat fringe that hangs over his forehead. His eyes are gentle and of a dark violet color with paler rings of lavender around their edges, and he's usually seen with an expressionless face.
In the Anime
Tanjiro's ancestor was a good friend of Yoriichi and arguably was one of his only true friends. Therefore Yoriichi gave the earrings as a gift, and since then they have been passed down the generations until they reached Tanjiro.
Later it is revealed that he married fellow slayer Kanao Tsuyuri, In the Modern World, Tanjiro and Kano had Great-great-great grandsons named: Sumihiko Kamado and Kanata Kamado.
Tanjiro wears hanafuda earrings that have the image of the rising sun over a mountain. According to Wikipedia, Hanafuda means “flower cards” in Japanese and are a style of Japanese playing cards that are smaller, but they tend to be stiffer and thicker than Western playing cards.