Continue of Parent's Getting a Divorce

You ought to tell her that her behavior is hurting your esteem and admiration for her. That she is jeopardizing your ability to trust her, that you see her actions as harmful to other members of the family. If she continues, after you have told her this, then distance yourself from her. She needs to tangibly know/feel that you do not support or condone her behavior.

That they get a divorce is separate from you. However, even when they are divorced, they still are members of a family... She either needs to realign her values and priorities so that they are not harmful to your family... or you and other members of your family will need to distance yourself from someone who is creating a toxic environment and threatening its stability.

I agree with Dee T. He needs to let his employer know what's going on and then see if he can get a restraining order against her.

let dads work know this woman is trying to do this and threaten her with her job , sounds like u need a no contact restraining order fast

I hope that I'm reading your post correctly. Are you speaking about your mom and dad? Are they married and living together? I assume they are if she is upset about the possiblity that he cheated on her. If he did nor did not cheat on her does not matter if he loses his job. Does she realize that she is only hurting herself as well if he loses his job?
There are other ways to deal with the issue than ruining the family financially.