Could I take my brothers children if they are in an unsafe situation?

I hope this is not too all over the place. So my brother and his wife split up recently and their children ages 8,7,5,4 live with their mother, who has been snorting bath salts, drinking, not feeding the kids, not providing a safe place for the kids. Their dad (my brother) has no job, is living with his friends who do drugs and drink all day long, has no way to provide a safe place for them to live. He is not patient with them and has a bad temper. The mother uses her kids a a pawn to stay on her section 8 housing, food stamps and other welfare. She has sent the kids to other family to stay stating that she "is done with it all and wants to live her new life without them" and then takes them back days later. My husband and I want to get the kids and provide them with a safe loving home but I am not sure if I would have the right to take them. Any advice would be greatly appreciated. I am not looking for people to talk bad to me or put me down in any way, I just need help. The children need help.