
Yoriichi never had children so Tanjiro is unrelated to him. Tanjiro's mark original mark is a burn he got as a kid and I think it was explained in an earlier chapter that the mark can appear if they're in contact with the person who had the mark first. In this case, both Tanjiro and his father met Yoriichi so it could be why they have the mark. And from there it spread to the other pillars

1 where do they say Yoriichi did not have kids?
2 Yoriichi died at age 80; his twin upper moon 1 has lived for about 400 years so 320 years longer this now the present... there is no way Tanjiro or his dad met Yoriichi unless there is time travel breathing, lol
3 what we do know is those earrings, the dance and the breath of the sun has been passed down for generations along with the hafuda earrings that Yoriichi and Tanjiro's dad wore and Tanjiro wears now

My bad, I confused Sumiyoshi for Tanjiro's father since they look exactly alike. But everything else I said was right. Yoriichi met him instead of Tanjiro's dad, but it's stated in the 170s that Yoriichi never had children and in ch 99, Sumiyoshi states that Yoriichi never had a successor for his breath of the fire god.
so basically:
1.) Yoriichi never had children. He invented the Breath of the Sun, the original breath
2.) His twin, Upper moon one, can't use said breath, he uses Breath of the Moon which Breath of the Mist is a derivative of. Making the Mist pillar related to them.
3.) Sumiyoshi, Tanjiro's ancestor is the one that met Yoriichi and passes down the techniques of the Breath of the Sun as the Dance of the Fire God. The earrings and the dance are passed down in hopes of finding someone that can handle the techniques of the fire God. Yoriichi and Tanjiro are unrelated.
4.) The mark on Tanjiro's forehead is a scar from childhood and develops into the demon slayer mark under certain conditions.
Is Tanjiro Yoriichi's descendent?