His character has been hurting for so long that he doesn't even know that he is hurting anymore. The only way he could survive was to detach himself from everything. After digging to find the edited and improved version of chapter 103 with his mother not even trying to fight to live/ignoring him and his ultimate goal of getting his father to just see his mother; and then how the father states how disgusted he must have been at his mother . . . I wanted to hug him even then.
And yes as we see, this chapter confirms that Tsurumi wanted him to shoot his brother and in chapter 164 he looked a bit uncomfortable talking to Tsurumi about his brother. Ogata with that formal posture, like when has he ever tried to look proper to an authority figure? Was the test with the Russian POW another check from Tsurumi or a check from Ogata to see if his brother had what it took to do the dirty deeds the 7th would embark upon after the end of the war? If that was a test, and he failed, than his death was back on the table.
Yes, you as the reader respect the fact that his brother had compassion for his Ogata and told him that he couldn't be the type of man who could kill with out feeling and it gives the feeling he honestly loved Ogata. But the fact that he could stand on his high horse and state that to maintain his purity required him to not harm anyone but instead inspire others to do the same in some ways could be interpreted as even worse. That makes his brother as hypocritical as their father in my eyes.
Add in the fact that you learned in chapter 139 that Admiral Koito tells Sugimoto that Hanazawa left him a letter around the time of his "suicide". There is no way that was an honest letter stating that his foolishness was absolved due to the purity of his beloved son (again total denial/ignoring his other son) and likely the letter written by perhaps Tsurumi to recognize Yuusaku as a better individual than his father, but again ignoring Ogata, thus allowing Tsurumi to further deaden Ogata to the world. It it is quite clear that Tsurumi manipulates everyone around him to use them to his own gain e.g. Tsukishima, Inkarmat, Tanigaki
I find it very interesting that once he deserts, he holds a grudge for a long time towards Tanigaki b/c he thinks that he killed his comrades, which is so out of character for him. Then when he gets super cruel and emotional to make Tanigaki to beg for his help (during the "Fugitive Tanigaki" chapter) and gets even more upset when Tanigaki implies all he knows is how to kill to solve a problem. I assume Tanigaki's personality is like his brother and likely made him more upset than his usual business like behavior.
The vision of his brother turning around and bleeding/crying while looking disappointed as he's pointing out his humanity and that look of disbelief/shock on Ogata's face was maybe him regaining his humanity or realizing he's human again and perhaps recognizing that finally in Asirpa?