So to answer the first question. no. Yoriichi is not Tanjiro's dad, that would be Tanjuro. And Yoriichi is not related to the Kamado clan at all.
Tanjiro's connection to Yoriichi is not through blood relation, but through their similar appearances, which is due to the divine nature of Sun Breathing.
Tanjuro Kamado was the name of Tanjiro Kamado's father. He passed away before the event of the main story of the Demon Slayer.
While Yoriichi and Tanjiro are not related by blood, they are related through the incredible gift of wielding the Sun Breathing technique. This is the most powerful breathing technique, born and gifted to Yoriichi and Tanjiro with the sole purpose and ability to defeat Muzan, as no other breathing form can.
As the battle reached its climax, Tanjiro was able to knock the doll's head off and discovered that the mechanical body contained a mysterious sword. Fans of the manga will recognize this sword as the one carried by Yoriichi Tsugikuni himself.
No, they are not related.
Some of the characters who have faced Yoriichi and survived
This happened due to a treatment that had gone wrong. While he was being treated, Muzan killed the doctor because he was not able to observe any results.
Despite not being a key character in Demon Slayer, Tanjuro had an important part in Tanjiro's life. Tanjuro was proven to be a remarkably powerful person, despite not being a demon slayer and having a sad sickness that renders his body terribly feeble.
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 ...
Tanjiro and his father look extremely similar to each other. Fans think that Tanjiro was related to the legendary swordsman since he had the same earrings, and their appearances are similar as well. However, Tanjiro is not a descendant of Yoriichi Tsukiguni.
The warrior Muzan feared was a swordsman named Yoriichi Tsugikuni. Yoriichi was the only slayer before Tanjiro who came close to killing Muzan, and the flashback of their fight occurred in Chapter 187.
In Demon Slayer, Tanjuro mentioned that he never felt tired while performing those moves. However, Tanjiro seems to have a limit when he performs the Breath of the Sun. This could serve as a form of evidence supporting the fact that Tanjuro was possibly stronger than Tanjiro.
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.
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.
As it turned out, the scar on Tanjiro's forehead did have some significance to it, rather than simply being a Todoroki-esque burn from scalding water. Tanjiro wasn't born with this scar on his forehead. Rather, he acquired it when tackling his younger brother out of the way of a falling pot of boiling tea.
Muzan Kibutsuji has done some terrible things in Demon Slayer, but his slaughter of Tanjiro's family is one of the most mysterious.
Moreover, Tanjiro's appearance somewhat resembled Tsugikuni. So the only reason Muzan is afraid of Tanjiro is because of the Hanafuda earrings he possesses, which acted as a reminder of his downfall.
Muzan hid after being almost killed by Yoriichi. I think the last one to actually saw Muzan before the events of the Manga/Anime was Yoriichi's brother before he turned into a demon. After long years of hiding, Tanjiro was the first demon slayer in centuries to see him again.
When Yoriichi moved forward to kill him, Muzan used the remains of whatever power he had left and divided his body in a powerful burst. Though Yoriichi was able to destroy nearly all the fragments, the pieces he missed escaped and allowed Muzan to regenerate again.
Yoriichi would be able to defeat every single Hashira on this list without breaking a sweat. Such was his reputation and skill in swordsmanship.
Yoriichi was powerful enough to defeat Muzan; however, he couldn't do so. That's because he couldn't come down to kill his twin brother, leading to his own demise. Even to this day, Muzan is scared of Yoriichi.
Nezuko is at least stronger than Daki, meaning that if Muzan could bring her back under his control, she would certainly qualify for the most prestigious title a demon can hold: a member of the Twelve Kizuki. Thanks to Nezuko's remarkable strength, she would have to be an Upper-Moon.
In the Demon Slayer Corps, the Hashira is a group of the strongest and most reputable swordsmen who have defeated members of the Twelve Kizuki. Yet, for some reason, Tanjiro Kamado, the series' protagonist, never becomes a Hashira.
Unable to fight back, Doma realized he was tricked but it was too late. He was soon decapitated by the combined force of Kanao and Inosuke, avenging Shinobu and her family.