I am not sure where to start but I will give it a shot. When you say that you want them enrolled as a guest, what exactly do you want them to be able to do? Are they auditing the course as if they were a student with the ability to participate fully in any activity or as a guest that can just view what is happening in a course?
If all you want them to do is be able to view the course as a guest, meaning they can't participate in any of the activities, you don't even need to create any accounts. The guest role is used, for the most part, to allow access to courses for those that have never logged into the site. To accomplish this, just go to your course settings and allow guest access with an enrolment key. When they access the course without logging in they will see an enrol me in this course screen that says:
"This course requires an 'enrolment key' - as a guest
you must enter it each time you enter the course. You should have received it from (course teacher name)" After they enter the correct enrolment key they are allowed to enter the course as a guest.
you must enter it each time you enter the course. You should have received it from (course teacher name)" After they enter the correct enrolment key they are allowed to enter the course as a guest.
If you want them to be able to participate in all activities then you can create some guest user accounts, enrol them in the appropriate courses and just give the guest users the username and password and let them login in and participate in the activities. After the 7 days change the passwords and you should be good to go. If you need more clarification just let me know.
I would also recommend that you remove the users that you assigned at the system role level. Generally you don't want to assign users at the system level.