Athena, I'm so sorry that you are experiencing this. Many of us here know how difficult it can be to support a person we care about who is suicidal, especially when the information about what to do is not easy to find. Here is a link to a page from an organization that has support and ideas about how to help a suicidal person. Please get support for yourself as well as your father. He needs more support right now than one person alone can give. Please see if you can find other family members or friends of his who are willing to educate themselves with you about how to support a suicidal person, and enlist their help, as well as professional help and group support. People must inform themselves about what has worked best for others in these situations. Being around a suicidal person is a very high stress situation. Kudos to you for reaching out. It is one of the most important things you can do. Please keep reaching out, for yourself and for your father.
The link page below has some good information and more good links below it:
And here are a few other tips as well:
You cannot "guilt" someone into staying alive, by telling them it would be cowardly to die, or that they are obligated to stay alive. Suicidal people need support and compassion and good listeners who can help them find their own reasons for wanting to live. It is common knowledge that "suicide contracts" do not work, i.e. "I, so and so hereby swear that I will not suicide, signed, so and so."
Drugs are complex and need a lot of careful moderation and supervision by people who are very careful, caring, and well educated about what they are prescribing. The person who is taking the drugs should be listened to very, very seriously if they feel that they are being harmed or not being helped by them. There are only a few well known drugs that consistently have an anti suicide effect. Lithium is one of them. Many antidepressants list suicide as a "side effect." Suicide is fatal. Drugs can be very dangerous and they are never enough by themselves.
Advances have been made in therapeutic techniques such as EMDR and other methods that involve the nervous system or the body in some way, in addition to talk therapy. EMDR can be enormously helpful for safely discharging the intensity of obsessive feelings and memories.
I agree that you should be directly in touch with your father's therapist and state your concerns very clearly. If you do not feel that you are heard or taken seriously, look elsewhere immediately and use the word "emergency." If need be, inform the person that you are writing down what they say, and always make sure to get their name at the beginning of the conversation.
Shame, humiliation, hopelessness and self blame are very toxic. The link above addresses a bit of the major importance of finding a way to help someone without shaming or humiliating them. People who are experiencing strong suicidal ideation do not generally know how to help themselves, at least not consistently and efficiently. They need guidance. They need to find hope. They generally cannot bear being subject to the pain of those around them. They are in extraordinary pain already. Sadly, they can be exhausting and very difficult to be around, which is another reason for getting lots of support.
I hope that what I have shared here is helpful, for you and your father. I am so very sorry that you lost your sister, and I am lighting a candle for you and your family, right now, before I send this. May you find the small light of warmth and comfort that is heading your way, and breathe it in...