Responses
- The big bro never suspected before, it shocked him too. Here.
http://www.mangago.zone/read-manga/the_inheritance_of_aroma/mf/c007/26/
- It's a big change, right? Shinobu went out to see Takezou right away after he met his wife and intended to do it for the last time. That means his wife somehow can threaten/blackmail him which we need to wait for more details.
Really, i don't see how the wife figured them actually scientifically confirming they're real brothers would change anything. Seems big brother always suspected anyways and little brother probably knew. Maybe she just wanted to see pain in the big brother eyes.
They're already in a clandestine gay relationship with their emotional (and actual) brother. And they've had a three way with the son. Top "sin" level has been reached and it doesn't seem to have bothered them.