
Then you are a pedophile

Asami x F/Mikhail x F/Yoh x F > F x Tao

I don't recall seeing that info in the manga. Is it part of the story in one of the novels (which I don't have access too)?

Thanks for the lead, perhaps it's due to the translation but after reading the story I didn't read anything to show that Yantzu is Tao's father. If anything it reinforced the feeling that Feilong simply has a strong affection, in a fatherly sense, towards Tao. Had Tao been a blood member of the family I don't think he would have ended up a parlor boy/servant to Fei.

Maybe it is but in the English translation, it's clear that Tao is Yan's child. Near the end of the light novel, Fei was worried as he saw that Tao, growing up, physically resembles Yan more and more. About why he ended up as a servant, I am curious about that too. I think no one apart from Yoh, Yan, and Tao himself knows that Tao is his nephew. Fei was hesitating whether to let Tao get involved in Baishe, he wanted to protect Tao from his world even though Tao decided he'd follow his master.
Maybe (this is just my guess) it is to conceal Tao's identity? If his subordinates and the outsiders learned that Tao is related to him, somebody might be targeting him.

Yan and Fei are not biological brothers, so there's no barrier to a relationship between Fei and Tao.

I must not have found the right story. I searched and read this one http://sakurayuki523.tumblr.com/post/137254045638/stigma-in-the-finder-i-finder-no-rakuin. It's the one where Fei and Yoh meet aain after the events in the maanga. But I can see your point about protecting Tao's identity. He's too sweet to let grow up to be a Baishe.
Everyone's saying they want Asami x Fei long but I'm just like any Fei long x Tao soon?
Edited : oops it was my fault for not mentioning this of course i mean when he's older like the one in Fei long's dream not underage