Are the deities mentioned in Hindus' holy books like Ramayan and Mahabharat unreal??Are they just stories??Is God of Christians Jesus Christ unreal??
Or they all are aliens who visited earth in the past??

Well, to start off, it's hard to prove something that is unreal. You cannot exactly try to prove a negative. It's like trying to measure cold. You do not measure cold because cold doesn't really exist, you measure heat. Cold is the absence of heat.

As far as religious belief goes, you cannot exactly prove the non-existence of a deity. The only way to prove if a deity exists is that...they do have to exist or else, what do you have to work on? So far, other than texts of a couple hundred years old, we do not have a way to measure whether or not these deities exist.

Religious beliefs are oftentimes subjective and based solely on personal experience and this is technically flawed for many reasons but primarily due to human perception. You and I perceive things differently. You and I most likely would not react the same to a stimuli. If we both touched the same hot pan, you may scream or cry or I may try to put my hand in water or panic.

I would like to think that if something is factual, the experience is the same for everybody else regardless of whatever personal differences there may be. It seems to me that no deity ever exists because there are thousands of religions and some even have hundreds of gods. If there were a god or more, wouldn't you think at least one would have graced us with their presence if they truly exist? Then maybe atheism would no longer be a thing because there would be concrete, irrefutable proof that a god exists.

The universe is vast and theoretically, the universe is continuously expanding. I'd think that the probability of life outside ours is more likely than the existence of a deity.

Hey. Are you familiar with the teacup theory? I forget the details, but there is a teacup on the other side of the sun in an orbit perfectly opposite to Earth so we can never see it. Even if we went looking for it, it is really too small to find. But I believe it is there and real because it cannot be proven that it does not exist therefore it must. It was put there by the FSM. (Just Google it).

Peace!

The Ramayana is an oral story in 5 parts enacted also in theatre or dances and later made into 7 books. Most of it seems a made up metaphoric story. For example, The king of Lankra had 20 arms and 10 heads and can't be killed by any other God.
Other figures like Jesus or Muhammad seemed like they did exist however fact seems diluted with fiction in their lives. For example where Muhammed split the moon or flew to heaven on a winged beast with a woman face.
With Jesus the Bible claims he walked on water, calmed the wind and ascended into heaven from his disciples on the mount of olives.
Although we cannot prove this as fact or fiction, we can discern with reason what is true and what is ficticious.
At the end of the day it down to individual interpretation as to how they perceive each religion. But since reading so much on religions, I cannot personally follow any faithfully with no real proof. It is futile to go along with a religion on a basis of a what if it could be real scenario.
What we do know is the world was very different back then with a more primitive way of life under superstitious moral stories even in a secular sense written by ancient philosophers. In the modern world we have more education available that has revolutionised how we think which has moved people away from needing religion as a fundamental basis for living their life.

Mythology already has a meaning and all religions/belief systems fall under the term. Humans had no way of properly explaining the things that were unexplainable to them at the time. The only way they could wrap their heads around these "supernatural" occurrences was to impart that experience through stories, which then evolved to scrolls and then books. What modern humans decide to project onto that speaks more about them due to their clearly perception driven projections.
I'll also add that any pantheon that creates a deity to keep the masses in check, through guilt or fear, does so knowing that both emotions are easy ways to control human animals.

I'm agnostic for one main reason -

Each religion asks me to take the word of other men's definitions of "God".

Historically, some of the greatest atrocities have been committed by men, not "God", in defense of their versions of "God"

I'm not arrogant enough to "decide" who God is, nor define Him - which leaves me the question of what this undefined God wants of me.

My fool-proof answer is to accept that there is a God, and that this all powerful entity chose to present himself to each culture in way that each culture could best understand him.

Assuming each culture has distorted God over time to conform to it's own bias, I then filter out the commonalities of each religion, for a probable set of spiritual guidelines -

Good will, the Golden Rule, empathy, kindness, forgiveness and self awareness - these traits, among many others, are "God" to me.