Lay out the vine leaves and place one quail on top, skin-side down. Season with salt and pepper. Put the rice, chopped walnuts and sultanas on top of the quail. Place the other quail on top and wrap in the vine leaves, leaving the legs protruding. Wrap in foil and seal both ends. Place on the barbecue and cook for about 40 minutes, turning the package every 10 minutes.