Through the J-Novel Club Priority Pass monthly group buy, you read official pre-publication light novel chapters at a shared cost per slot. The plan currently available is the 1-user (private) plan, where you pay the full slot and receive shared credential access. The group plan with up to 2 people per group is still in preparation, so for now only the private slot is open.
Because this is shared account access via credentials, there are rules to follow: do not change the password or email of the account, and do not forcibly log out other devices as it disrupts other slot members. Also do not add your personal payment method to the shared account. Violations will result in admin removing your access from the slot without compensation.
If you choose the group plan once it opens, your order will enter a queue and the account will be activated once the group is full. Until then, your payment is held and only processed when all slots are filled. For the 1-user (private) plan currently available, activation happens immediately after payment is received, without waiting for other members.