To answer your question, it only takes two Natural gametes, male and female, to create an Atheist, since everyone is born lacking a belief in a God or Gods.
No supernatural being is required, nor does one exist, M’Lady. *Tips fedora.*
(I finally broke down and bought a fedora to make official my Smug Atheism. A Nice black pleather one. I deliberately bought it small to make my head seem bigger. Back in my college days in the late Eighties, I had a fedora and I was an Atheist, but I never associated the two and the Internet wasn’t ubiquitous enough to widely spread the Smug Atheist in a Fedora meme. Did I help create that???)
It takes one god less than the number that a theist believe exists. There are about 30,000 gods recorded in human history. Christians are atheists when it comes to 29,999 of them but insist that their one is real. I don’t believe them. I often ask them to tell me why they don’t believe Zeus is real and then I use their answer to explain why I don’t believe that their god is real.
Yes, we are all born atheists and stay that way unless indoctrinated by brutal marketing campaigns.