For all that I don't PVP, I like the idea. However, what you've proposed for the team challanges:
Daomei (Leanon)
seems clunky and time-consuming to me. I suggest keeping official consent/denial to just the leaders of each team, and maybe the seconds too, at the most. Edit: Some sort of system notification (like PVP tagging notifications?) with a countdown to team PVP would be useful too, I'd think. An option ought to be included in the dueling code to allow for team challenges. I suggest that once a team leader challenges somebody for duel, and that character is member of the team, a dialogue opens asking for either "normal" duel or team challenge. If team challenge is chosen, every member of the challenging team has to accept or decline the challenge. In case someone declines, the team leader has the option to turn down the challenge, or proceed, in this case the disagreeing member is removed from the team, same for idling members who do not respond during a timeout period.
Once the dueling is accepted inside the challenging team, the challenge is sent out to the challenged team. Here, the team leader is asked whether she is interested in a fight. Now, all members of the challenged team are asked to accept in the same way as in the challenging team before. On successful completion, lists of players in both teams are exchanged together with a request to start the fight (or abort). After that, the fight may start.