I remember this being on mangafox. The summary is two brothers live together then they take in their younger brother. Even as a child they are both obsessed with him. The youngest boys father also happens to be his mothers brother. That sort of thing seems to run in the family.
There was some sort of weird explanation for the incest.
Like the family was decended from priestesses that mated with some sort of shapeshifter.

The last chapter I remember was after one of the brothers had kidnapped the youngest and chained him up.

Sorry for the lousy summary.

I think it's Nibiiro no Hana Gou. I love that manga, great drawing and smexy lol.

Moved to Yaoi/Yuri~