Being the grown up

My dad passed away 11 years ago which is a long time. And yes I've accepted that fact and of course feel sad sometimes and miss him still. But him passing away kind of made me the head of our very small family there's only me and my sister and our children my sister is older by 2 years but has had extreme mental health issues far greater than mine. She also lives far away.Just today there was a big issue in her household with her oldest son that is impacting her and her youngest son. But as much advice as I can give and as much authority I can impose its not enough and all I can think is if my dad was here he would sort this out everyone in question would listen to him and do as they are told. I can't fill his shoes and there is noone else who could either.