A side - kick system has been mentioned which would allow characters of a lower level to play with high level characters without disadvantage. (news.mmosite.com)
Joining someone's room will be odd as they might have higher or lower level character than you and probably on a different quest as well. (gamepur.com)
Besides that, I took care of leveling his characters because my dad hated the grinding. (theswitcheffect.net)