I'm a fourth year law student in Australia.
I have been thinking about this for some time in respect of my time spent serving and donations given to another cult - Vipassana meditation as taught by Mr S N Goenka.
If a gift is not freely given, then it can be recovered by way of legal action claiming undue influence. I should think that would be pretty easy to prove. If you leave you'll go to hell and be shunned to boot. So you stay. If you stay you feel obligated to give the money. So it's not freely given. As for the "ministry", well that is obligated also by the WTS for a JW, so it is work for the society, again not freely given. A class action quantum meruit claim would probably sink the Watchtower Bible & Tract Society completely.
If a child is born in the [present] "truth" they don't exactly have a choice in the matter - are they to live in "the world" - having as their father satan the father of the "lie"?????? Where is the free will in that?
I consider that it would have to be something like the class actions against Dow Corning or James Hardie - I'm sure it would have good prospects of success and the idea should be raised with the lawyers acting already in child abuse cases.
In actual fact if any family members of JW's who have died and given all of their estates to the WTS want to recover as well they should also consider joining such a class action as gifts in a will are subject to the same legal principles.