How to determine if a public key point y is negative or positive, odd or even?
There is no concrete determination that makes one 'y' value negative or not in an EC point. Feel free to make your own convention, like y-values &lt;= than half of p are negative, and &gt; half of p are positive. That's just a convention, though.
Related:

What does the curve used in Bitcoin, secp256k1, look like?



Also, how can you identify which pub key is odd and which is even?
ex: private key 1 x,y is odd , private key 2 x,y is even

You can't! Not without knowing the private key itself. If you could, you would be part of the way towards solving the discrete log problem.