As said above you can't really group ride and train at the same time unless the whole group is following the same training schedule. Ride with the group once a week and on your other rides implement a training schedule that will achieve your goals. There is plenty of training information online or you could spring for a coach to design a plan for you. It will include zone two riding ( alot ) and then turn into High intensity intervals. Sounds to me like you first step is to work on your endurance and base training with the Zone 2 rides.