Parent Destroying my life and others with their mental health

One parent is going into what seems like a manic episode after being depressed and I and others feel like my parent is no-polar or at the very least needs medical intervention. But this parent refuses to see it and won't get help as what they are saying and doing in their mind is 100% fact and true. It is destroying the other parent and their character is now in question by police due to the other parent stating what they beleive in their mind is the truth when it is not. It is destroying my family and affecting my life personally. The parent with the mental health issue is basically attacking the other parent with the law, with words, is attacking me with accusations and words that are hurtful. The accusations are unfounded and disgusting and cruel that this parent currently experiencing some mental health issues is involving my sibling who is mentally disabled and needs full time care. I feel this parent is now using my sibling and using the law to attack the other parent which is downright disgusting, yet I cannot do anything as the parent will not seek help and I cannot get help for them unless they are causing physical harm to themselves or others. My parent is harming others with the law and accusations and using a defenceless mentally impaired person/child to their own advantage. What do I do? I'm at a loss for what to do I have been told that nothing can be down until this parent wants to seek help or causes harm to themselves or others. I don't want to wait till someone is hurt and at this stage I would not put that past this person.