Enrolling multiple sims?

All you have to do is enroll one sim. After that, choose a random destination (doesn’t have to be at the university) then travel with the sims you want to enroll.
Once there, activate cheats with “testingcheats true” then shift click each sim you desire to enroll And click “university debug” there will be an option to enroll selected sim. Boom.

If you want to enroll a sim that is not in your family then simply travel with them, turn on testing cheats and shift click and “add them to family” prior to the university debug. You’ll be done in less than a minute!!

You can use cheats as "university debug" or "add to household", etc... Otherwise without cheats, as some already said, you can simply enroll one then go to manage world to change from household and enroll the other sim, moving them in the same dorm, and keep going for as much sims you want to enroll at the same time.

I played a couple at UBrite I wanted for the story to meet at the uni and end up together. I first enrolled the guy, then I went back to play with the girl's household and I enrolled her too. I moved them in different dorms at first because I've set gender dorms. I switched from one another for a while (a quick way I used was going through cheats : using "modify in cas" once there when I went back my active household switched on the sim I just had in cas). Then when they became boyfriend/girlfriend I added the guy to the girl's household in order to them to live in the same dorm room.

It also works if your students want to live in one of the student houses.