To unlock all the animals for Director Mode you need to get all peyote plats that are on land (you do not need to get the ones that are underwater, as those animals are not in Director Mode). That is a total of 21 plants.
You can easily find the plants on
http://gta-5-map.com/ (select the peyote plant icon on top - light blue with a circle on it). Look at the screenshot to see if a plant is on land or underwater.
After this you need to play as one of these animals in Director Mode.