Mystery Verses

I'm hoping one of you can answer this for me and uncover this mystery.  Why are these verses in the Bible? I’ll say what I think is that some monk added this verses in when he was translating the Bible thousands of years ago and these verses were not supposed to be in the Bible. I don’t know why God allowed them to stay in the Bible though. 

Mark 16:17-18, "These signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues; they will pick up snakes with their hands; and when they drink deadly poison, it will not hurt them at all; they will place their hands on sick people, and they will get well.”

But not all believers drive out demons and speak or pray in tongues.  And definitely no believers pick up snakes and drink poison and survive, at least I've never heard of anyone successfully doing that. 

And then there are these verses, John 20:22-23, "Again Jesus said, ‘Peace be with you! As the Father has sent me, I am sending you.’ And with that he breathed on them and said, ‘Receive the Holy Spirit. If you forgive anyone’s sins, their sins are forgiven; if you do not forgive them, they are not forgiven.” What?

So the disciples received the Holy Spirit twice?  Why?  Once here and then a second time at Pentecost?  Also verse 23 seems very odd, like I it really seems like a Catholic monk inserted that verse.  It sounds like a very Catholic, and not Biblical, thing to say. It does not seem to line up with the rest of Scripture.  Why would someone be able to hold forgiveness from someone else?  Why would any person be able to forgive the sins of another?  Can't only God do that?

I have a footnote in my Bible that says Mark 16:17-18 is not found in the earliest manuscripts of the Bible.  So did some crazy monk really just sneak in those verses too just to confuse people? Like maybe Satan told him to do that. As well as the verse about humans being able to forgive or not forgive sins?  Because how much confusion have these verses caused?  People literally try to pick up snakes and drink poison because of that verse.  And then in Catholic churches people rely on confession time and their priest forgiving their sins, but can't only God alone forgive our sins?

So I think these 4 verses are not supposed to be in the Bible. But I would love to hear thoughts on why they are or should be. 👍🏼😉