My role and responsibilities as aunt (or, thought work vs. action)

My brother and his ex-wife are very acrimonious and combative toward each other, and my 8-year-old niece is caught in the middle. She is forced to try to appease these two adults whom she splits her time between. I’m very worried about her and I love her fiercely, but I don’t know how involved I should get. They live across the country from me; I see them in person a couple times a year and talk on the phone frequently. My niece is exhibiting some troubling behaviors, and I’m terrified that it’s just going to be all downhill from here for her. Her parents both earn their money illegally, and I suspect that there are some mental-illness considerations in play. Even though they have put my niece, their daughter, in the middle of their ongoing war, I do believe that they are decent parents in a weird way, in that her basic needs are met and she feels loved. But I can see that their war with each other is causing my niece great stress. As an aunt, I’m unsure about how I can help–or whether I even can or should help. I don’t have children of my own, so I don’t have an instinct for what’s helpful and appropriate and what’s not. I’ve told both of them individually and collectively about my concerns, and they don’t deny that they’ve created a bad situation–but then they both go immediately into explaining why it’s the other one’s fault. I’ve offered to pay for family counseling or individual counseling for my niece, but they always say “no thanks, we don’t need it.” I’m confused about whether I need to do thought work on my own thoughts about this or whether I need to take some action. Or both? My attempts at Models haven’t rung true for me. Any guidance would be so wonderful. Thank you!