I read your other thread. You mentioned your middle son has academic issues even though he works hard. Have you ruled out learning disabilities? Your eldest could have executive functioning issues which would make organization, studying, and keeping track of homework difficult. I’m sure there are smart but lazy kids, but kids with these issues are often labeled as lazy.
There is one thing I’d ask if he were my son. Was it his choice to leave college? I’d make sure he’s not running from a bad GPA or academic probation. Those things are fixable, but sometimes kids are too embarrassed to tell their parents they failed.
Your son isn’t moving home to crash on your couch. He’s arranged for a place to live and has a job. Those are good things. I hope he’s living with other college kids. It won’t be long before they’re talking about internships and jobs. That may motivate him to think about his future. However, before he moves make sure you’re clear about what you’ll pay for and what you won’t. If he were my son, I’d pay for health insurance, doctor’s visits, and prescriptions. I wouldn’t pay for a car (insurance, registration, gas, or repairs), rent, food, cell phone, or personal expenses. He should have those costs in front of him now so he can start saving.