say if my dad is giving qurbani for me on my behalf will he need to let me know that he is giving qurbani 4 me or is the qurbani classed as invalid if he didnt tell me?
If your father wants to offer Qurbani on your behalf then he must seek permission from you. Otherwise the Qurbani will not be valid on your behalf. Your father get the reward of sacrifice but you would have to do it again.
The approval may be given verbally or through someone but it has to be done with your knowledge and permission.
And Allah knows best.