Paul W. Fairman 
Ten From Infinity [EPUB ebook] 

Excerpt: "There was nothing unusual about the traffic accident victim with a broken leg until intern Frank Corson found he had two heartbeats. He thought that strange, but not as strange as passing the identical man in the street a few minutes later. One by one eight identical strangers are discovered, five dead, and each with two hearts. Eight artificial creatures, identical in every respect down to the fingerprints, and none of them human. They claim they are the vanguard of an alien invasion. And there are two more on the loose. To stop the destruction of the human race, we must stop the… Ten From Infinity."