The great tribulation
Intro
I believe that the great tribulation will be 3.5 years long and that the two witnesses will be around during this time as well as the dragon, the false prophet and the beast.
3.5 years
We can see these 3.5 years on three verses in the book of revelation.
(Revelation of John 12:14 [KJV]) And to the woman were given two wings of a great eagle, that she might fly into the wilderness, into her place, where she is nourished for a time, and times, and half a time, from the face of the serpent.
In Revelation 12:14 we see time and times and a half (time=1, times=2, and a half=0.5, 1+2+0.5=3.5) which sums up to 3.5 years.
(Daniel 12:7 [KJV]) And I heard the man clothed in linen, which was upon the waters of the river, when he held up his right hand and his left hand unto heaven, and sware by him that liveth for ever that it shall be for a time, times, and an half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.
The a time, times, and an half can also be found in Daniel 12:7. I think it is talking about the same time.
(Revelation of John 11:2 [KJV])
[2] But the court which is without the temple leave out, and measure it not; for it is given unto the Gentiles: and the holy city shall they tread under foot forty and two months.
In Revelation 11:2 we see 42 months (42 months = 12 + 12 + 12 + 6 months = 3.5 years) which is 3.5 years.
Revelation 13
[5] And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
In Revelation 13:5 we see the 42 months mentioned again, indicating that the great tribulation is 3.5 years.
The two witnesses
Revelation of John Chapter 13
[1] And I stood upon the sand of the sea, and saw a beast rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy.
[2] And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and great authority.
[3] And I saw one of his heads as it were wounded to death; and his deadly wound was healed: and all the world wondered after the beast.
[4] And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
[5] And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
[6] And he opened his mouth in blasphemy against God, to blaspheme his name, and his tabernacle, and them that dwell in heaven.
[7] And it was given unto him to make war with the saints, and to overcome them: and power was given him over all kindreds, and tongues, and nations.
[8] And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world.
[9] If any man have an ear, let him hear.
[10] He that leadeth into captivity shall go into captivity: he that killeth with the sword must be killed with the sword. Here is the patience and the faith of the saints.
[11] And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.
[12] And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
[13] And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
[14] And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
[15] And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
[16] And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:
[17] And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
[18] Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.
I believe that the two witnesses will be Enoch and Elijah.
(Revelation of John 11:2-4 [KJV])
[2] But the court which is without the temple leave out, and measure it not; for it is given unto the Gentiles: and the holy city shall they tread under foot forty and two months.
[3] And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.
[4] These are the two olive trees, and the two candlesticks standing before the God of the earth.
The basis for this is that its assigned for men to die once.
(Hebrews 9:27 [KJV]) And as it is appointed unto men once to die, but after this the judgment:
So David for example who has already died once cannot come back.
Enoch has never died yet, it seems.
(Genesis 5:24 [KJV]) And Enoch walked with God: and he was not; for God took him.
It seems also as if Elijah has never died.
(II Kings 2:11 [KJV]) And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven.
Of course it is possible that the two witnesses are two new people that have not been around before also but I believe that it will be these two.
Daniel
(Daniel 12:1 [KJV]) And at that time shall Michael stand up, the great prince which standeth for the children of thy people: and there shall be a time of trouble, such as never was since there was a nation even to that same time: and at that time thy people shall be delivered, every one that shall be found written in the book.
The great tribulation seems to be mentioned in the book of Daniel in Daniel 12:1. Also it says there that those who have their name written in the book shall be delivered.
So I interpret that as that Gods people will be delivered during the great tribulation. So there is no need for Gods people to fear I guess during this time. Also there is no need for a pre-trib rapture since Gods people will be delivered.
Now some of Gods people at least are beheaded in the great tribulation, so beheading could be a way to be delivered.