I'm really sorry to hear about your sister and how she has decided to choose addiction over her son and family--I am also, sadly, not surprised.
Please don't hesitate to vent away here anytime you need! We get it!!
Many prayers and much love to you, your nephew and brother-in-law. I'm so glad your nephew has you in his life and on his side!
Many prayers, too, for your sister that she may finally find her way to a better future without addiction.