If he is truly getting help. Maybe he needs different meds or a different therapist. Support group would be good too. Where he can talk to others going through what he is going through. But it also sounds like your parents are definitely enabling him. Maybe his issues have to do with his parents. Are they willing and open to go to counseling with him? Cutting him off will not cure his depression, but make it worse. He needs family support. Maybe if the whole family went to counseling with him? But by him laying around, not working, letting them support him, that is not helping him either. He needs a job so he will feel he is making a difference and give him some confidence in himself. If he cannot find a job maybe he could volunteer helping others. A homeless shelter perhaps or a dog shelter. If he could help out at a homeless shelter, he will see how bad others have it and make him grateful for the family and support that he is so lucky to have. That might make him quit feeling sorry for himself. Exercise helps with depression.
Is they keep supporting him financially, he will never learn to make it on his own. But they should continue to help him emotionally. He's resenting them because he does not want to get out and try to find a job. It's easier being taking care of by them. He's working them and it sounds likes it's working for him. I feel he has some issues with self esteem. Maybe he needs someone to go with him to help him look for a job.of course not into interviews or anything like that. But just to get him started. Go to workforce with him. Losing a job is a big hit to self esteem. Maybe there is something he is doing on the job or not doing that is getting him targeted for layoffs.
Try looking up and studying SELF-FULFILLING PROPHECY. in more simpler terms, it is "when one feels they are no good or unworthy, they will behave in a Way that will illicit behaviors and actions from others that will CONFIRM their negative feelings about themselves. Ex. Leads up to getting fired.