They are the two unnamed older brothers of Fuyuto and Kyōshirō. Thair names were never mentioned.
Ginga Densetsu Weed[]
They and their mother were constantly abused by their violent father.
They and their siblings were adopted by a traveler who offered their father a boar in order to take them with him so he could take care of them and make an end to the abuse. Apparently, the traveler took good care of them but they left him when they heard their mother was ill.
The three brothers returned to their home, only to find their mother's skeleton. Bitter towards their father, they were sure he killed her and wanted to kill him in order to make him pay for all he did. After long time of searching they found him and trapped him in front of a cliff.
The two older brothers told Kyōshirō to stay put and live, as they didn't want their youngest sibling to become a murderer of their own father.
Then, the two brothers committed a suicidal attack by pushing themselves and their father off the cliff. They did this because a killing of one's own father was a horrible crime and they didn't want to live after committing it.
After that, Kyōshirō found and buried their dead bodies together with his mother.