Hello and welcome to PsychCentral! I'm sorry you are dealing with this most difficult situation. Since I've not been in this situation myself I doubt there would be much of anything in the way of insight I could offer. However here are links to some articles, from PsychCentral's archives that may be of some help:

https://psychcentral.com/blog/11-way...one-in-denial/

https://psychcentral.com/blog/helpin...snt-want-help/

https://psychcentral.com/blog/4-ways...th-depression/

https://psychcentral.com/lib/10-ways...hos-depressed/

https://psychcentral.com/blog/how-to...essional-help/

https://psychcentral.com/lib/how-can...hos-depressed/

https://psychcentral.com/blog/common...y-be-suicidal/

There's also a book I have seen recommended as a "must read" for anyone who has a family member with mental illness who can't, or won't, seek treatment. It is titled I'm Not Sick, I Don't Need Help. (It is available for purchase on Amazon I believe.) Here's a link to a review of the book:

A review of "I'm not sick, I don't need help!" - Friends for Mental Health

My best wishes to you...