stolen trees

YIKES, It sucks when these issues have to do with family.

I dont know what the family dynamic is in other areas of your relationship with them but since they have not honored your request to stop cutting to this point I would retain a lawyer have him / her draw up the document outlining your wishes. I would pay to have that served ( is it possible to have that document on file in the courts should you need to take this further) and I would also mark all the cut trees to date so that if any more are cut they cant give the excuse that those were previously cut. Basically this has to be an information gathering / documentation drill so that if you need to prosecute you have plenty of proof to make it stick.

Hope it works out on a positive note
joe