Alyssa Ashcraft, a senior at the University of Texas at Austin, does not have nearly as much space now as she had in her apartment, which she left after the campus closed. Now she’s back at her parents’ house in Nederland, Texas, near the Louisiana border, sharing her childhood bedroom — and childhood bed — with her older sister.

Navigating each other’s sleep schedule is one thing, but the bigger challenge, she said, is when everyone is awake. Ms. Ashcraft, who still has her job with the university’s alumni association, is working from home, as are her parents, who are both schoolteachers.

When she needs her space, Ms. Ashcraft takes her laptop to the porch. And in a throwback to childhood notes telling parents to keep away, she tacks a small handwritten sign on the door that says “I’m in class” or “I’m in a meeting,” so that no one goes outside.

Still, confrontations in their cramped house are inevitable, and often hark back to old-fashioned sibling rivalries: arguments over who gets to use the TV, music playing too loud or a mess in the kitchen. “I feel like sometimes I’m 18 years old again and I have never left,” Ms. Ashcraft said. But, “I just have to remind myself that this will be over one day and I will get to continue building a life for myself outside of my childhood home.”

In the month since she returned to Swarthmore, Pa., dragging a large suitcase, Phoebe Rosenbluth, a senior at the University of California, Los Angeles, has mostly stayed at the home of her boyfriend’s family because her parents, who live nearby, turned her bedroom into an office after she started college. Ms. Rosenbluth has visited her family every day, using the time to paint with her 15-year-old brother and reconnect with her parents.