NTA

You need to protect yourself and your life.

However, you should sit Mia down and explain everything to her in detail. Tell her none of this is her fault and that you are suing because you have to, not because you want to.

Tell her that she always has a place with you and you will always be there for her not matter what happens because she is like family to you.

Tell her you know things are hard right now and that with the lawsuit they may get harder. But adults sometimes say and do things that are horrible in order to try and get what they want, and when that happens you have to stand up for yourself and with that comes consequences.

Tell her you will always be there for her, and that you are open to talking about anything she wants to share with you as the lawsuit goes on. Let her know the outcome that will probably happen to her dad and the rest of the family should this continue and let her know that you have tried to keep it from going that far but her fathers own actions are what is making this have to happen.

She is old enough to be told these things honestly and understand them. Also, not telling her like this opens the door for doubts later on from her dad pouring poison in her ear.

Take the opportunity to explain the difference between loving someone and being In Love with someone.

I really hope this all works out for the best, because it will be one of those situations where you do everything right but things will still be messy after.