separated from family for uni

If yoy move one into a dorm you will have to concentrate on that sim for a while. You can rotate between the 2 but you may want to pause enrollment for the student whilst playing the main household. Alternatively, you can have the sim attend university from home rather than move them into the dorm.

My sim already got accepted, I would like him to go to Foxbury and the invitation letter says he has to attend they welcome to see him there. After that can I move back home and he finish uni at home? sorry I ask too many question I just don't want to separate them unless there is no other way.

He shouldn't have to move out or attend anything other than classes if you don't want him to. I would suggest enrolling, assuming you haven't yet, making sure he doesn't move out. He should be fine. I don't remember that message but you could send him to the Commons and to the information booth to learn things about student life.

Yes, you can send your sim to Uni and then back home afterwards; your other 2 sims will still be there. However, as Mariefoxprice said, your sim does not have to move out. When choosing a dorm, you'll see an option to stay in your current home. You don't have to separate anyone if you don't want to.

When I sent my Sim to university, it separated her into her own household. Her family was another household. When my Sim graduated, she was still in her own household. I moved her back into her family's household. It didn't do it automatically, but it was easy.