Hello, StephB -
I know a little bit about Willowbrook and had thought that all issues had been settled decades ago when the surviving residents were resettled elsewhere. I'm truly sorry to hear that there are such heart-wrenching loose ends. The ex-Willowbrook residents I knew all had family involvements, as far as I know.
I'm sure you are aware of this book, but if not, you should read it for background:
The Willowbrook Wars: Bringing the Mentally Disabled into the Community by David J. Rothman & Sheila M. Rothman.
I found these two sites that deal with the same issue you are:
Blog for people in the same situation: Willowbrook State School -- A Voice Behind the Wall
http://www.willowbrookstateschool.blogspot.com/
NYT article: Trying to Flesh Out the History of a Family That Was Minus One
http://www.nytimes.com/2008/05/08/nyregion/08towns.html?_r=2&ref=todayspaper&oref=slogin
All the best.