I have 3 monkey and 1 serpent statue, but in library there are 5 spots for statues? and what about nector? or incense? could some kind soul help me!!

yes you need 4 monkeys. Did You get the one from the room with the six doors where several combinations are needed to open one after the other? The incense you get from the golden serpent statue after giving a golden coin and the nectar you gain in squeezing a spideregg and collecting the stuff in a empty bottle which you can find in the kitchen. Good luck
Junglegirl