How Do I Get My Brother On Disability For His Major Depression And Anxiety That Keeps Him From Working (and Functioning)?

I have a brother who worked for the government for about 7 years. He got vested with this retirement system after 5 years. Things were goin good until he began to have sleep problems. He could not sleep even with very powerful sleep medicines. I'm not sure but I think this is what made him get depressed over time. He used to be so clean and on time for everything. He just was never the same person from one day on. Fast forward to more recently (last 6 months) he has major depressive disorder (diagnosed by not 1 but 2 psychiatrists). Since then timeframe start he just lays in his apartment all day not working and orders takeout for all food. His dirty laundry piles up and he hardly ever sleeps.

Disability benefits are available from his former job even if a person resigns/is terminated for up to 72 months after the date of separation (note they stopped working about 6 months ago). I event went to my brother's HR department in person with him and the HR and also the benefits person was their and they were very comforting of my brother. They said there are benefit programs they can try and stay on the payroll and use up their remaining sick leave to attend those programs and my brother with a flat affect face he has developed from major depression said "I just wan't out. I cannot work anymore." With that he was marked as resigning. The benefits person haded us a disability insurance for both short term and long term disability my brother took out when he started with that department 7 years ago. It says a lot and we will have to read it.

I think my brother's best bet is to apply for both SSI and SSDI. He has over the 40 credits to get full disability. He also has about $10k saved up in a low cost of living area. But with rent being $1,500 and everything else like his car costing $600, etc he will run out of money soon. We need to get him on SSI and/or SSDI and then once approved on that look into the disability plan my brother still is eligible for even after resigning.

Any thoughts on this? I was unaware major depressive disorder can get you full disability payments both SSI and/or SSDI.