Even though you can invite multiple users to the same subscription, a subscription can only be managed by one admin. If the admin no longer can continue to manage this, you can claim the subscription from him.
To claim a subscription, click on your avatar in the top right corner, go to Subscriptions and click on Claim subscription:
Fill in the name of the admin from who you would like to claim the subscription.
An email will be sent to the current admin to ask him to approve your request.
Once the admin has approved your request, you will be the new admin of the subscription.