I am looking for information on nicknaming all three characters, how Stepan and Yakov would address Nikolai when they first met, and after they became closer, and what Nikolai would call Stepan and Yakov.
Right now I'm calling Stepan 'Stepka' from Yakov (as I read that the -ka endings come off as teasing and were generally used between close friends, but please tell me if I have misunderstood this), but I'm not sure what to call Yakov from Stepan's perspective. Would Yashka or Yaska be appropriate from Stepan's perspective? I've read that -enka and -ochka come off as parental in Russian, so would Nikolai call Stepan 'Stepenka' or 'Stenka' and Yakov 'Yashenka'?
I've done a lot of reading on Russian nicknames. I've found an article that straight-up lists diminutives for hundreds of Russian names, an article about using diminutives as a foreigner and Russian expectations, and other similar articles- they generally list a few diminutives and what would be appropriate for strangers, friends, and family. None of these articles have contained the sort of specific information I'm looking for in terms of appropriate nicknames from siblings. Furthermore, I am still unsure of how Stepan and Yakov would address Nikolai after they became closer (my understanding as that they would call him Nikolai Alekseevich at first). Is there a specific title for older family friends, or does aunt/uncle work in that role as it does in the Philippines?