Pieter Paul Easy Bank is enough to create or to partake in a single Joint account. Easy Money+ allows creating and partaking in multiple Joint accounts.
"+1" or "Joint subscription" are old, deprecated plans that are no longer available, and that allowed you to (among other things) use a Joint account, but the plans have been streamlined a bit more since then. "Premium" is also no longer a thing, but it doesn't matter if you have an Easy Bank, Easy Money or Easy Green plan, all of them allow usage of Joint accounts. The only difference is in how many you can use at the same time.