It's hard when you are an adult and your parents divorce. You want to help. You want to know what is going on.

It's hard to stay out of it and not take sides. But that is what you need to do. For your own sanity.

My suggestion is to be there for your younger siblings and to make it clear to both of your parents ( and your grandmother) that you will not be put in the middle of your parents' divorce. And remind them of that everytime they start to involve you.

Go back to school, get your degree. Focus on you and doing what will help you in the future. Your parents are grown, they can work this out for themselves. And should without involving their children, even the grown ones.