Thought of writing this because for sure, you have questions right now. Lol. So here goes nothing ~
Jungkook and Namjoon are step brothers?
First. I just changed that to 'half brothers' because they can't be step brothers if Jungkook's parents already died. Well, it can be. But what I really meant was 'half brothers'. Just forgot to edit it before I published the chapter. So about that, Namjoon's mother and Jungkook's mother was the same. The first family was Namjoon's. She (mother) gave birth to 2 children (Namjoon and his sister) and later on decided to leave them because Namjoon's father was beating her. She tried taking her 2 children but her husband didn't let her. That's when Jungkook's father met Namjoon's mother. They lived together and gave birth to Jungkook later on. It was just 4 years ago when Namjoon knew about Jungkook. They tried to keep him since his parents already died but Jungkook, being the stubborn he is, left Namjoon's house. He went back to their own house. That's when Jungkook met "him". 'He' helped Jungkook in any way possible.
How did Namjoon got involved in Jimin's kidnapping case?
Remember when Jimin tried blocking Jungkook's number because he got scared of Jungkook? He did something on Jimin's phone (how did he got Jimin's phone? - suspect's among the three, remember?) so that Jimin won't really be able to block Jungkook. (I don't know if this is possible. This is FICTION guys. Haha) That's how he helped the two. I can't tell in details how he helped the two because you still don't know who the 'guy' is. So~ haha. I might do a part 2 of this once I revealed the 'guy'.
Can't think of other questions. I'm not feeling well too. (Stupid allergies) So if you still have questions? Just comment it. I'll answer it as long as it's not about that 'guy'. Hahaha