Probably; for much of history (including in Shakespeare's time) it was illegal to be an atheist, so most non-believers would probably keep very quiet about it!
In more recent times; several Nobel literature laureates are openly atheists and one of the greatest philosophers in history (Bertrand Russell) was also a non-believer.
Probably; for much of history in Europe atheism was illegal, so non-believers tended to keep quiet!
Someone please help me
William Shakespeare of course, who else would have. There's always been an argument in the background that Shakespeare was the "Front Man", and the plays were actually written by someone else, with a variety of names being suggested.
Who is Garfield? I guess someone not very famous.
Almost certainly yes; atheism was illegal in Europe for many years, so non-believers kept very quiet! In more recent years, many modern artists are openly atheist.
There is no organized group called "Atheism." While there are several atheist groups, there is no membership requirement for atheism. An atheist is simply someone who does not believe that gods exist.
An anti-Stratfordian is a person who believes that someone other than William Shakespeare wrote the plays to which he is credited.
Shakespeare didn't write most of his work down, and was transcribed by spectators of the audience who wrote down what was happening. But Shakespeare is the author of his works, but probably did join with other writers.
Sometimes you can make good in a line of work totally different from your father's.
No. That was the plot of the movie Shakespeare in Love. In fact the story of Romeo and Juliet was much older than Shakespeare, and it would be just as ridiculous for someone in Shakespeare's day to have claimed it was about them as it would for someone today to do so. "I've written a story about Romeo and Juliet in 2013 and it's based on my life experiences." Sure it is.
Apart from William Shakespeare? The truth is that everyone without exception in Shakespeare's days and 99% of people now know that Shakespeare wrote his plays. The other one percent have weird notions that someone else wrote Shakespeare's plays. In the 19th century it was Francis Bacon. Nowadays it is more likely to be Edward de Vere. It doesn't matter because it is impossible that Bacon or de Vere or anyone other than Shakespeare wrote them.
If you have the money, you can travel the world interviewing people to find out if they have heard of either one. My guess is that you will have to go into some pretty remote jungles to find someone who has never heard of Shakespeare.