I had a little time on my hands, so I decided to convert the old Playerbots to the new TrinityCore structure. There are still some things not quite working, but I may try fixing them when I have the time. There is a sql file located in sql\extras that you can execute for the playerbot NPC. There will also be additional configs added to your configs file that you might want to check out.
Download: Playerbots.patch
Note: It's a patch file, not a bunch of C++ files. Anyway, I hope this helps somebody! Have fun.
How it works
Basically you are able to bring your other characters from your account and have them assist you in. They are able to also participate in quests with you as long as you tell them to accept the quest.