How do you "know" the answers to those questions?
Same as with anything, really. There are 3 types of modern day Christians. Each of them claim the Bible as the basis for their beliefs. The majority are the traditional, modern day apostate Christians. They are the ones who may or may no attend church and the majority of their beliefs come from the church's long history of adopting pagan (outside) influences. These teachings are very old, primarily from Babylon, but introduced by Greek philosophers and the like. The immortal soul from Socrates, the Trinity from Plato, the Cross from Constantine, hell from Dante and Milton, Christmas from Dickens and then the Rapture from Darby. Greek teachings began to infiltrate Jewish thinking during the campaign of Alexander the great in 332 B.C.E. and Constantine's influence became Christian theology in 325 C.E. I think I have those dates right. Close anyway.
A lot of modern day traditional teachings outside of those philosophies also took hold in the Dark Ages when Bible dictionaries and encyclopedias were popularized from the thinking then, like for example, the expanse being a metallic dome surrounding the earth with sluices for the rain.
Then there are the fringes of Christianity. These are what you normally see on forums such as this. They like the mass appeal of Christian theology, the basics. But they add individual aspects of mysticism, metaphysics, psychology, and science.
Then there are the Bible purists. Those who dismiss the outside influences and investigate the Bible's true and authentic teachings without those influences. Those are Jehovah's Witnesses and myself, who's beliefs are very similar to the JW's.
All you have to do is cut through the nonsense, which is pretty well documented, and get to the truth. How do you know if you've got it? If its all harmonious with scripture. For example, we reject that the soul is immortal, as Socrates taught (Plato, quoting Socrates - Phaedo, Secs. 64, 105, as published in Great Books of the Western World (1952), edited by R. M. Hutchins, Vol. 7, pp. 223, 245, 246.) which is harmonious with Ezekiel 18:4 / Matthew 10:28.
You check that with even mainstream traditional modern day religious and secular sources, like . . .
“The Christian concept of a spiritual soul created by God and infused into the body at conception to make man a living whole is the fruit of a long development in Christian philosophy. Only with Origen [died c. 254 C.E.] in the East and St. Augustine [died 430 C.E.] in the West was the soul established as a spiritual substance and a philosophical concept formed of its nature. . . . His [Augustine’s] doctrine . . . owed much (including some shortcomings) to Neoplatonism.”- New Catholic Encyclopedia (1967), Vol. XIII, pp. 452, 454.
“The concept of immortality is a product of Greek thinking, whereas the hope of a resurrection belongs to Jewish thought. . . . Following Alexander’s conquests Judaism gradually absorbed Greek concepts.”- Dictionnaire Encyclopédique de la Bible (Valence, France; 1935), edited by Alexandre Westphal, Vol. 2, p. 557.
“Immortality of the soul is a Greek notion formed in ancient mystery cults and elaborated by the philosopher Plato.” - Presbyterian Life, May 1, 1970, p. 35.
“Do we believe that there is such a thing as death? . . . Is it not the separation of soul and body? And to be dead is the completion of this; when the soul exists in herself, and is released from the body and the body is released from the soul, what is this but death? . . . And does the soul admit of death? No. Then the soul is immortal? Yes.” - Plato’s “Phaedo,” Secs. 64, 105, as published in Great Books of the Western World (1952), edited by R. M. Hutchins, Vol. 7, pp. 223, 245, 246.
“The problem of immortality, we have seen, engaged the serious attention of the Babylonian theologians. . . . Neither the people nor the leaders of religious thought ever faced the possibility of the total annihilation of what once was called into existence. Death was a passage to another kind of life.”- The Religion of Babylonia and Assyria (Boston, 1898), M. Jastrow, Jr., p. 556.
. . . and you've got a pretty good grasp on the truth.