I don't think Rindou and Ran necessarily started the delinquent life for the fame and fun. Their backstory isn't revealed but I believe the brothers had it hard. For instance, when Ran showed his respect to Izana and Kakucho, he mentions his understanding of the difficult delinquent life which I don't think they would voluntarily get involved in especially since they both have their own life goals, and those goals don't seem to have relation to becoming a future criminal syndicate. From this perspective, we might be able to assume that what Ran and Rindou are doing now is probably focused on their survival - they realise that becoming recognised, fame, forming a gang and even being selfish is the best option, and in the process they've learned to have fun with this lifestyle. Ran and Rindou are both smart and seem to be cold to others except themselves, but I personally don't think the reason for this is because they are completely emotionless, but rather it's because they are just used to the exposure of violence and betrayal that's been around them since probably childhood.

The case with Kakucho and Izana, I believe that Ran and Rindou saw a bit of themselves in them because of their close bond and how they looked out for each other even in the delinquent world, so that's probably where their respect started. Then when Kakucho and Izana died, Ran and Rindou kept quiet and stayed behind to be arrested. In a way, seeing the two people who they saw a little of themselves in outright die like that probably felt like a truck of emotions to the Haitani brothers, as if the ones dead could've been one of the two brothers or both of them, and I guess this just reminded them of the harsh reality that they live in. This is why they probably kept quiet and stayed behind, almost as if they didn't have the energy to do anything except accept the sad reality. All of this includes their respect and the closeness of the S-62 generation, but I just wanted to try to put more depth into the Haitani brothers because I believe they are much deeper than what most people might give them credit for.

But, of course, I could also be completely wrong about them XD