Will full cup of apple seeds kill you?

This vary from Apple to Apple, and also very much between the type of Apple.

Most Apples have between 8-12 seeds, but some have less, others have many many more.

The amount of seeds may vary with the condition of the tree, and the growth year also. If it is a particularily bad year, then there might be more seeds and fewer Apples. In a good year, the Apples will be bigger and have fewer seeds.