No. Atheists do not believe in gods, because gods do not exist as theists describe them to be. The rules that the gods are credited with delivering to humans were composed by humans - community leaders.
Atheists can follow rules. Most atheists follow the rules of state law. There are very few atheists convicted of crimes compared to Christians convicted of crimes in America - why do so many Christians have difficulty following the rules for good community???
Why were you unable to recognize this simple argument to your proposal?
I disagree with your second sentence. How do you know God or gods do not exist to lay down the rules for objective morality? Isn't it your faith in no God nor gods that makes you believe and state what you just stated? Atheists generally say they want proof, but no evidence is satisfactory for them.
As for your first sentence, I can only speak for Christians, but one of the rules and the first one from the ten commandments is:
You shall have no other gods before Me.
Not believing in God or gods would violate rule #1. Disbelief is a sin.
Plenty of verses in the Bible about disbelief --
What Does the Bible Say About Disbelief?.
Christians believe Adam committed the first sin by disobeying God and eating a fruit of the Tree of Knowledge of Good and Evil. It was a negative test. Today, we have the positive test of John 3:16, "“For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life." However, this rule is not followed and is too difficult for atheists to believe. This wasn't made up by humans, but by God.