I worry about my parents and my siblings

My parents have always argued in front of my older siblings and myself. We grew up having to go to the furthest room in the house and sing songs really loud to drown out their yelling. There is an 8 and 10year gap between myself and my younger siblings. I spent my teens trying to protect them as my older sisters did for me.
I feel as though my own struggles with depression and anxiety stem from my parents unhealthy relationship. Now that I am doing better for myself (counselling and off medication) I worry that my younger siblings may be developing similar issues.
My father works overseas so we only see him for a few days every 2 or 3 months. Similar to other long distance relationship ships , loyalty is questioned. I don't want to believe my father would be unfaithful but the things my mother has said during their arguments don't sound so made up. Today i heard her threaten him over the phone with her own life. I did not react straight away. I'm just keeping an eye on her. I know my father, he is stubborn. I know he would think that she's just saying it for attention but I also know my mother and I know how hurt she is.
I want them to stop arguing, even if it means they seperate/divorce. I want them to see a counsellor but how do I talk to them about it? How do I get them to help themselves?
My little sister has cried to me once before because she's scared my mum will hurt herself.
What do I do? How can I help them?