I'm trying to hand the website over to someone as I've left the guild. When I try to relinquish powers, I only receive 4 people (out of 50 accounts) to choose and none of them are the GM.
They need to make sure that they have an account on the DKPSystem.com main site with the same email address.
Second question... how can I make sure that the next administrator cannot renew the subscription with my credit card on account?
There's actually nothing special you have to do. The data is not stored at all, and whatever data IS stored, is not retrievable by website users, including the original creating user. So that data is fully secured.