As of 04/24/2023:
1) You can manage your payment method, billing address and cancellation of your group membership in your profile on the PC/Web version.
2) You can see in your profile on the PC/Web version who is part of your group rate. In this overview you will also find the codes that are still free, which you can then give to friendly hunters so that they can join your group rate.
3) You can increase and the number of group members or delete one member of your group and reuse the free slot for another member.