This thread is cold.
OP - it is reasonable to be angry at your sister. But, if she doesn’t want to, then she doesn’t want to. Which sucks. But she could at least agree so that you can take her.
I find family values have gone out of the window and it’s sad. Strong families are the foundations of all communities- we know it deep down.
We’ve somehow made teens and children appear to be horrible monsters. But umm, we were all teens once and we were all kids once. And I am sure we have adults that have shaped our world views.
I am there for my kids, and OP, your nieces mum/ your sister sounds like she really isn’t in a good place. But if something was to happen to me, one of my prayers is always that my children stay in safe hands. And that someone at least in the family takes them on.
So I think, yes, as family, I think uncles and aunties should look out for nieces and nephews, and support where they can. I have seen it in my family. I’ve even taken on a kid for a short period of time. It’s bloody hard work, but set some structure, get to know the kid, get support.
Maybe this is part of the individualist society we’ve become. It’s every man and kid for themselves? ,