Castellum If someone is already on the easyMoney plan, you can easily add them to your own sub-accounts via Connect or create new Joint accounts with them. But if they're not a bunq user and don't plan on becoming one, you can also use bunq +1 to either add them to an existing sub-account via Connect or create a new Joint account together with them. This is not free, you'd have to pay 2,99 Euro/month for each user that you add as your +1, but the other user doesn't have to get any special plan. They of course still have to download the app and enter their details.
Make sure you check out the relevant Knowledge topics and the Pricing Sheet so that you know exactly how the feature works if you plan to use it. Your +1 can even get their own bunq card and one free ATM withdrawal each month. However, while they are your +1, they won't be able to open up any sub-accounts of their own.