I THINK how it works is that the version 3 copies of the program allow multiple logins, while the older versions don't.
The thing is not all languages are released in version 3. Spanish should be fine, it is the less popular languages where this is an issue. (we have Welsh, for example, where version 2 as as good as it gets).
oh btw my 4 year old and my 6 year old both use it independently. The only issue we've had is that I don't think you get THAT much language at level 1, and in Welsh you only have level 1. So we're having to try to find alternative resources, and there is simply nothing as good out there! (we have a big problem with Welsh-we live in Wales and so our kids are pretty keen to learn Welsh, but we are not Welsh speakers and there is NO access at all to child-level Welsh classes outside the schools)