I am worried about my nephews what should I do?

I have a 2 year old nephew and a 4 year old nephew. The home enviornment is disgusting and turned upside down. The house is a pig sty. The mother dotes on the two children all day. The 2 year old and 4 year old sleep with their mother while the father sleeps in another room. That is because the mother chooses to sleep with the children not because of a marriage problem. The 4 year old is using a bottle and still in nappies. The mother refuses to put him in preschool because she states that she does not have the money. But the mother has money to drink wine in the evening and smoke a packet of cigarettes per day and the father has money to buy junk food everyday. The bath tub is full of water the next day after the night before. The kitchen is turned up side down. When you enter the home you just see mess and throughout the house. You find it impossible to find a seat on the lounge. The 4 year old attends a child psycholgist and apparently he suffers from anxiety. The mother hardly goes out without the aid of the father. When the boys fall over she instantly attends to them. In the kitchen is dirty dishes, benches you can hardly see, The kitchen table is not useable full of mess they eat on the lounge, the rubbish in the kitchen is piled up in plastic bags and sits there for days. If the father does not take the rubbish out the mother refuses to do it because it is his job. I am very concerned about my nephews and the impact on the environment they are living in. I feel like I cannot say anything because I will loose all contact with my newphews because my sister in law is that type of person. She has lost contact with two of her sisters due to her sisters stating about her parenting.