How can I find out if a book is still under copyright without hiring a lawyer?

It's quite simple: all literary works are protected by the international copyrights laws till 70 years after the author's death.

So Kafka, Proust, Melville, Tolstoi, Twain are free (generally called "in the public domain") while Freud, Kerouac, Sontag, Nabokov, Capote and Brecht are under copyright even they are dead.
Therefore it seems you can't publish the stories without the rights owner consent, be it the publisher, an estate or a greedy relative.