Parent is an addict - temporary injunction?

I know a guy who is a relapsed addict and in complete denial. His clean/sober friends have all begged him to return to inpatient treatment, but he insists he can "do it himself". He has part-time joint custody of his children and is in NO CONDITION to be in charge of these kids. He deals drugs at his home and uses while they are in his care. His children have previously witnessed him o.d. himself into a coma and has since gone through treatment and relapsed again. We want to tell the mother and stepfather to not allow the children to go visit with him but also want to give her a legal way to immediately protect herself because he will spin a web of lies to convince her that we're lying to her. (He is very convincing, too). Plus, he's going to fight her tooth and nail. So... would the answer for the mother be to file a temporary injunction to stop the visitations? Can the authorities force him into treatment? At this point, the authorities need to intervene for the safety of these kids and for his safety as well as his in endangering everyone. His sober friends say he is on a "suicide spiral" and have never seen things this bad before. Thanks for your help.