Andzelika You can use Joint accounts on the Easy Bank (€2,99/month), Easy Money (€8,99) and Easy Green (€17,99) plan. Both of you need a bunq account, and both of you will be billed. So if you're both using Easy Money, you'll be separately billed €8,99/month.
This isn't specifically for the Joint account, you're paying for the bunq plan you're using.