macos - Cannot remove group rights on Mac OS X folder

I have configured two user groups on Mac OS X Server (10.5.8): Administration and Personnel. I've been using chown and chmod to set the group rights recursively on folders. Now I notice that the Personnel group has "custom" rights on the main Administration folder.

I want to delete the "Personnel" group by right mouse clicking the folder > get info and press "-" after selecting the group, but this is not working. I guess this is caused because the subfolders and files in subfolders als have the "Personnel" group rights and I need to delete these first.

Is there a terminal command to recursively delete a group from the folder and file rights?

Thanks!