Seeking help for teenage nephew living with mum with BPD

Hi everyone,

I'm new to this forum, thanks for having me and allowing a safe space to ask for some advice.

I've got a teenage nephew who lives with his single mum (my sister in law) and I've got some real concerns for his own mental health. My SIL has previously told us she has BPD, bipolar disorder and depression, however she no longer seeks professional help as she now denies she has a mental illness. Her manipulation of family from fear of her outbursts have scared most of the family away and she continues to burn any friendships very quickly due to her behaviour. We have tried to help her in the past and have ended up getting verbally abused and it never goes anywhere. She receives financial support from her parents but they are elderly and scared (*and broke- financially and emotionally) and finding it increasingly hard to help her.

Her son has almost completely stopped attending school recently and has begun to have outbursts of his own (likely due to being an emotional teenager and understandably living in a very volatile environment for a long time), however and I'm very worried that her lack of insight into her own health is impacting on her ability to make safe and considerate decisions for her son. She does not have the emotional ability to help him, and thinks all of this is due to him being a teenager and nothing to do with her.

He is receiving some counselling support from school, however I know that they will not be aware of the whole story of what is happening at home.

I guess my questions are...what can we do as a family for support her son? He turns 16 next month, can he choose to go and live elsewhere? What are his rights?

I know she will adamantly refuse for him to go anywhere but I believe it's in his best interests and safety, at least for now.

I hope this is the right place to ask

Thanks for reading and sorry for the long post.