Please explain differences of 'ella' , 'illa' , 'alla' as I am unsure in which context to use them.
ella' , 'illa' , 'alla all have the meaning of no, but I'm unsure about when to use them and confused.

Question

Answer

There is no word 'ella' to mean no(or it should be a different transliteration of 'illa')
I will try to explain the difference between 'illa'(ഇല്ല) and 'alla'(അല്ല) through examples.
Question:"Do you have children?(ningalkku kuttikal undo?)
Answer: "illa"(no, (I don't have any children)
Question:"Is that a bird?"(athoru pakshi ano?)
Answer : "alla, athoru pakshi alla(no, it's not a bird)

Question:" Do you know the answer?(ninakk utharam ariyamo?)
Answer :"illa,enikk utharam ariyalla"

So, generally 'alla'  is used to negate something ,or to say something is 'wrong'. In all other cases 'illa' is used.