Despite sharing a little facial resemblance, Tanjiro and Yoriichi are, in fact, not related. Nor is he a direct descendant of him. Both Tanjiro and Yoriichi can perform the Sun Breathing Style and wear the hanafuda earrings, but these are the things that had been passed down to Tanjiro from Yoriichi via Sumiyoshi and his descendants. Moreover, Yoriichi did not have any kids.  Hence, shutting down any debates regarding Tanjiro and Yoriichi’s blood relations.