With JoinBareng's Masterpiece X group plan, you only pay for one slot from a group of up to 3 people. The account used is a shared account with credential access, so the username and password are distributed to all group members. You will receive the credentials after the admin activates the plan and can immediately start creating 3D models within your share of the 750 credits per month package.
There are important rules to follow when using a shared account: do not change the password, do not change the account email, and do not log out other group members' devices. Doing so will cause other members to lose access and disrupt the whole group. Simply log in on your own device and use the service as needed, since the active login sessions are usually enough for normal usage.
Because the group plan currently open is the 1 user or private package, you get full access to one slot without waiting for a group to fill up. Group packages with even cheaper cost splitting are being prepared and will open soon. While waiting, you can still use the 1 user package to access Masterpiece X at a more affordable price than subscribing on your own.