My brother has a DD with a woman he had a brief fling with 8 years ago. He has always seen her but irregularly for much of that time as he was struggling with alcoholism and not in a good place himself. He has been sober for the last 2 years and is now engaged and settled with a steady job. I'm posting because he, while he agrees that the situation with his DD is in his words 'not ideal' he feels there's nothing to be gained by any action and I want to canvas opinions to see if I should continue to try and persuade him otherwise!
So onto the details. My DBro was quite young (19) when he met the mother (who was the same age). She lived in a caravan on a nearby new age traveller site at the time, though moved into a flat with DBro when she fell pregnant. Their DD was born after they'd only been together a year and they split when she was 18 mo though things were rocky for most of that time and they didn't live together from when she was 6 mo.
Since then the mother has returned to living on traveller sites. DBro used to travel to wherever she was staying to see DNiece but since he stopped drinking and cut association with his old friends on that scene, she has been coming to stay with him for a week a few times a year instead and so the rest of the family have finally been able to get to know her over the last two years.
DNiece lives with her mother, her mother's partner, her 2 younger siblings, and various dogs in a bus. They are living without proper running water, just a tap in the corner of a field, and with no proper toilets (hole in the ground ones 
[vom] ) and no shower/bath facilities. She is usually filthy when she arrives for visits as she goes weeks without a proper bath though her hair is looked after really well, strangely 
and I will say in her mother's favour that she never has nits.
She does not go to school. She can read and write and do basic sums but that's because she is a bright child, not because anyone has bothered to teach her. She is quite vocal in her opinion (I say her opinion, it'll be her mothers opinion but you know what I mean!) that school is a waste of time and her mother has apparently always said that no child of hers will go to school. Fair enough. But then she needs educating, not just running wild with a pack of children day in day out with the excuse that "she is learning what she needs to know"
She has no bedtime at home (the children apparently get told to come in when it gets dark), gets taken to weekend long parties frequently, her mother/mother's partner/their friends smoke weed in front of the children (according to DBro who used to see this when he visited). She really seems to love and relish the basic care she gets when visiting - bathing, hair drying, wrapping up in a towel, painting nails with my DD, choosing new socks and knickers, that sort of thing - and also the routine of 'normal life'.
DNiece is a lovely child, she has good manners and is very bright and articulate. I don't think she is being abused by any stretch, but I do think she is subject to persistent low level neglect and think my DBro should grow a backbone and talk to his ex about educating her properly, washing her, and at the very least finding somewhere to park the bus that has showers and toilets fgs. DBro thinks this would be out of order, he says he let her down and now has no right to tell her mother what to do, he also tells me that their lifestyle is different and that unless his DD is in danger he isn't going to wade in like that. I think he is being a spineless twit and it is never too late to stand up for his own child....