People are making things up as usual.
No, atheists cannot be spiritual. Spirituality requires faith in spiritual things and atheism is basically absence of faith in that. Atheists only believe in the physical realm. So atheists cannot take part in marriages, funerals, religious celebrations etc. as all of these are religious. It literally contradict atheist's belief to participate in these ceremonies.
Morality is different, though. There have been moral achievements done by secular philosophy, like the abolition of slavery and child marriage. However, a great deal of morality are still religious obligations.
I want to add one that no person is born an atheist. People become atheists out of their will. So they have been raised in religious households, and even after becoming atheists they still maintain the religious values, like giving money to the poor as an example.
Actually we are all born atheists. We learn things as we grow up and that is how we start to take in more and more religious background. May it be the explanation on how the world works or simply celebrating its traditions. Such as praying for strength in times of hardship, or marriage, or doing things such as holiday. Religion is a culture. It is not something inherit that is passed on through our genetics. Now there may be some discussions about "Souls" that is still unexplained to this day. As far as we are aware of, this soul is consciousness. This outlook may change as we learn more about our world both physical and nonphysical.
There are many scientific theories that are also in line with religion, may it be one of the mythologies or the ibrahimic series (monotheistic).
I think it is ironic to be atheist. Atheistic thinking is to deny a higher power is involved. However, they think of this as if it were a fact without having enough data. Its "data" is derived from its counter arguments of religion. "There is no higher power as I do not see an entity residing above us" which brings us to the notion of "faith"
Believing that there is or no higher power without any confirmation with data being gathered is to have faith. Faith in the unknown. Which kind of breaks the whole "atheism" concept that there is no higher power. As children we are unaware of this "higher power" argument. To us, adults are the higher power. They are the ruler. They dictate and are basically become our first concept of godlike beings. However, before all of that, we are not already thinking of higher power and the inner workings of the world. Thereby making us all start off as atheists. We act and react. If I can sense it, therefore it is. If not, it does not exist. We can see this logic with children when you place an object infront of them and they would acknowledge it but put something infront of that object, they think it no longer exists.
Much like how computers render. If it is out of sight of the viewer, it is no longer existing (removes it from being rendered to focus more power in other functions). That is how an atheist should act.