Is this sentence correct "All I need is you and I " ?? since "All I need is I" seems not proper here whereas "All I need is you" does.
Although it's correct, as Tim has pointed out, it's also very unnatural. Poets might be drawn to it because it's a playful repetition which gets us to focus on the meaning.
When you use I, you're usually employing it in the nominative case because I is the subject of the sentence:
but when you use me you're generally using it in the accusative case because I is now the object of the sentence:
The sentence is incorrect. You can think of is as a sort of equal sign, where you can put the subject as a predicate nominative and vice-versa and the sentence will be correct. Breaking it down, then, the subject, predicate, and predicate nominative are:
It should be (you could substitute we for you and I, if that helps to understand a bit better):
With a single nominative, it should read: