Agreed. Get a family law lawyer ASAP. Also, it would be helpful to you and to this lawyer if you started writing down a history of what has occured with your daughter, with as much detailed information as possible (dates of arrests, drug usage, inpatient treatment, *everything you can think of*). When you do meet with the lawyer, you can get him or her up to date on what's been going on.
If you can't afford one, look into legal aid in your area:
Nassau/Suffolk Law Services Committee, Inc.
As for the children, there must be some Al-Ateen literature or tween literature around concerning the addiction of a parent. They're going to need a lot of support through this.
As for you...have you considered individual counselling for yourself (or Al-Anon)? You're carrying a very heavy burden...
*hugs* I hope you keep us posted!