It doesn't matter if you believe a person existed. You can have sources which mention those people and it's the historians task to judge how reliable those sources are.
The Bible is, btw, not that much of a reliable source in many ways.
Especially in the old testament, there are SO MANY STORIES copied from the Babylonian myths.

You can believe in God and being Christian and stuff.
But please stop confusing facts with faith. It's annoying.
If facts don't fit your belief alter your belief. The most annoying thing, eg, is that some fundamentalists think, that accepting the matter of fact about evolution means you don't believe God created the world. Or think that the Bible was written by God. Do you even know how many people did translate that thing? Saying, that God was steering them while there could be no bad people... Man. It's ridiculous.

But yeah, the copies of a book make it more reliable. Hitler was right, as he sold so many copies of his book, than. Great.
It feels like talking to a teenager who discovered just recently the internet.