Dude, I got this.
As soon as their next appearence vesus the group occurs, Verry will be all "Headmaster! Best friends! I'm sorry. ;_; I hate my sisters for torturing your friends.", and come with us.
They'll plot more, but only fight us one last time before Helenos. Then "magic curse" will be broken, and the two will attack her, and then warp over to our side and join.