Sister with 2 kids wont stop using amphetamine - depressed & susceptible to paranoia

[Nose Dive]

My bill's sister keeps doing whizz and gets in an awful state when she does so. The worst thing is she has two kids and is very susceptible to paranoia. She's depressed anyway and this isn't helping. Her husband also does whizz and has done from the age of 14 and doesn’t intend to quit. She says that she dosen't want to do it but her husband is persuading her to. I'm at my wits end and have no idea what to do, please help.
I'm afraid something bad will happen soon if stuff isn't sorted out. What does my Bill do? Threaten to go to the police if she carries on? Threaten to call social services? Sorry about the quality of this post but I am very hung over, I will re-edit if I have time later.