Garnett there is a way in game in Borderlands 2 to level your new characters easily if you are playing on a console. Characters in your game regardless of level get appropriate exp to the level of the mob regardless of the level of the character in their party. You can tun on split screen start a new character and then go around with your main guy murdering things and they will level fast. Still can be a slog
Second the final boss on the main difficulty is level 30 you guys should be done play through no. 1 by now unless you are combing the world for everything.