Firstly you can't help someone who doesn't want to be helped. so, you create at environment where they feel safe to seek help.
Next Steps
Step 1- Breath, You need to come up with a plan of your own, like give yourself 21 days (and don't worry, it can't become worse)
step 2- start with day 1- you tell yourself you are not helpless (unknowingly you have stepped into his loop of feeling helpless, so you are feeling helpless). everytime helpless feeling over powers you , which it will. Turn your back to it. Start with home remedy. slip ot lots of water and remember his childhood favorite foods (do all this secretly. as depressioned people tend to distrust intention)
step 3- continue fav food thing (secretly) as long as you can.
step 4- incase you feel comfortable. Ask him to clean his stomuch by using home remedy like isabgol etc. (will balance the chemical a little and body will feel the kick (life instinct kicks in)
step 5- repeat your chanting that you are not helpless. you may succeed or may not in First 7 days. keep you expectations in negative.
step 7- repeat the fav childhood food thing.
step 8- take out old photoes. etc.
step 9- share your personal problem or make up a believable story that you need his help. and wait.
step 10- repeat all. 21 days. and see maybe he himself will seek professional help.
step 11- if nothing works, call elders of your family.