I really like the guild chat moderator new power. Also the kick+ and the fact you can only promote members up to their rank.
However, what do you exactly mean by "their own rank" how is this going to work?
To be honest I do believe there should be ONE power that allows the player to change guild news, guild interests, recruiting method and wither its opened or closed and finally the ability to create a rank with full power. This is how someone can really be called "co-leader" if he has all of those powers. Would you not agree?
You can customize each rank, and give specific powers that you want them to have. If you don't want co-leaders to kick each other, then you can disable kick+
I'd give Veterans promote, recruit, and kick powers. Members would have recruit and kick. That way, if there aren't any co-leaders on, the veterans and members could manage by themselves. A veteran can recruit someone, promote them to "member" rank, and now you have a mini leader and co-leader
Can change the name of ranks to whatever you want