Yes of course they can. That might be the wrong answer for some of you.
Let me qualify. Atheists can have a happy life. The afterlife however we dont know. Their eternal life is the question mark.
example... a moral ethical person raises a family with love. no huge dramas. no huge tragedies. Long and happy life. they try not to think about what will happen in the next life and just focus on this one.
I agree, Atheists can live happy lives, until they die anyway. However, if they die as Atheists, their eternal existence is not a question mark. For the word of God is clear about what happens to those without Christ. Anyone who does not believe is already condemned, which is the state of everyone who comes into the world. It is not until a person has faith in Christ that they go from eternal condemnation to eternal life.
As far as "moral ethical person raising families, God has already answered that question with, "there is none righteous, no, not one. All have sinned and all fall short of God's righteous standards. People are not saved by being moral or ethical or by raising families, but by faith in Christ as the One who paid the penalty for our sins.
There is no question mark regarding those who live and die without Christ.
"Whoever believes in him is not condemned, but whoever does not believe stands condemned already because they have not believed in the name of God's one and only Son." - John 3:18
"Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God’s wrath remains on them." - John 3:36
"For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life."
The above scripture means that, anyone who has not believed in God's One and only Son, will perish.
Remember what happened to the spirit of the rich man after his body died? He went down into Hades/Sheol where he was in torment in the flames. In Jesus account of this literal event, the rich man never asked why he was there, because he knew why. The only thing that he did request was to quench his thirst and to have Lazarus resurrect to go warn his five brothers so that they wouldn't come to that place of torment.
Once a person dies without faith in Christ, their record is sealed and they will be held accountable for every sin they committed instead of Christ. when a person believes in Christ, He was already held accountable for the believers sin. He met the righteous requirements of the law on behalf of the believer and He took upon himself the wrath of God that every believers deserves, satisfying it completely. When we believed, we were credited with the righteousness of Christ and reconciled to God. God sees the believer through the spectacles of Christ as being righteous even though we still have our sinful natures, because of our belief in the One who already paid the penalty for our sins.