Mari Tessa

Second dialogue.

English: Hmph... You never change. How much longer are you going to keep worrying our parents?

Japanese: Hmph... Still the same... Honestly, that's exactly the kind of guy you are. How long are you going to keep making [our] parents worry?

There's a very obvious change here. Katsuya judges Tatsuya's character in Japanese. He uses "お前というヤツは (Someone like you)", I translated it according to nuance in the sentences though. I'll break down the word choices.

お前 - you. Extremely blunt and familiar. Shows familiarity but as I mentioned in my original post, Katsuya doesn't normally use this.

ヤツ - there are a lot of translations for this. Some people just use guy, some people say it's bastard. Personally, either way, I think it's a rude way to refer to a person. Seeing the context here, we can tell that it's used to show how Katsuya looks down on Tatsuya's character.

Then we get to the last line which is Katsuya pointing out how worried their parents are.

But with the background context we have in the Japanese, it's not a matter of question anymore but a rough way of saying "How long are you going to keep doing this to [our] parents?"

Notice how I've been putting brackets in "our". Japanese doesn't require the usage of subjects or pronouns so the "our" is implied. Another interesting take on this is to say that Katsuya may not be using "our" but saying "your" as an extra blunt way to attack Tatsuya's character.

As if to say, "They're your parents too remember? Show some respect."

Third dialogue.

English: I'm not asking you to understand me or our father's position. But you have nothing to gain by running away.

Japanese: At this point, I don't expect you to understand someone like me or someone like father. But if you merely run away, you won't gain anything.

This is extremely loaded. Let's start with how Katsuya refers to himself and their father.

Katsuya says "この僕の事 (kono boku no koto)" to refer to himself. The usage of "kono" here is interesting because it shows that he isn't referring to himself but rather, he is referring to his stance or positionality, particularly from Tatsuya's perspective.

He does the same for their father he says "父の事 (chichi no koto)". That's a very formal way to refer to your father. He's not talking about their father as a familiar relationship but rather the position that their father is in.

There's distance in how he describes the both of them, especially in regards to Tatsuya. This is further pushed by how he says "今更 (at this late stage)" because he understands how distant Tatsuya is now from him and their father.

Then he goes to "理解してもらおうとは思わん (I don't intend to ask for your understanding)" as a sign of resignation. He understands that it's too late and they've gone too far. He knows that he can't do more for Tatsuya. The usage of 思わん is unconventional too, it shows that he's quite stern and old fashioned in how he's saying things.

Then we're hit with the last line, "But if you merely run away, you won't gain anything. " This is Katsuya's final plea to his younger brother. I just want to point out he uses "ぞ(zo)" at the end of the final line. It gives the impression of "hey, I'm telling you this seriously."