Hi mr1991. Welcome to Psych Central. I am sorry you face so many challenges with your dad.

I am also a partner to someone with mental health challenges that resists treatment, so I can empathize with your pain and frustration. What I say is based on my experience in the US. Check with people in your city and or country as to applicable laws and guidelines.

There is no magic tip for how to get someone who is resisting treatment to get it, even if it is obvious they are suffering from it. This being said, there are some indirect routes which may be a help. You hinted at one: use leverage to get the person to weigh the alternatives and possibly decide the lesser of two evils is better. In this case getting treatment rather than losing his wife or fouling relationships with children. This has to be done showing them the benefits of a course of treatment in maintaining their world.

If the house is not safe, local officials may come in and give them ultimatum to clean it up. Reporting them to authorities may have negative consequences.

Another way in US a person can be compelled to get treatment is if they are a threat to themselves or other by their action or inaction. This can be difficult to prove unless the person has reached a serious mental health crisis where they are no longer living in the reality that most people live in.

these may be of interest
How to Deal with Difficult Family Members

How to Deal with Difficult or Toxic People

How to Help Someone with Mental Illness Who Does Not Want Help

Feel free to message me or reply to this thread
@CANDC