Rudy,
    Since I was saved, all I ever thought about was things in a chronological order.
It wasn't until I was to teach Sunday school classes, that I realized that there were other possibilities, also.
            Gino
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7 Seals  -  7 Trumpets  -  7 Vials
Possibilities:
I.      Preterist: These all happened in 70 AD
II.     Amillennial: Allegorical of adversities in the Kingdom
III.   Futuristic:
       A.  Series
       B.  Parallel
       C.  Telescopic
       D.  Combined

Series:
That everything happens in the chronological order that it is given in book, as you mentioned
A problem with the sixth seal happening earlier on in the tribulation:
Isaiah 13:9 Behold, the day of the LORD cometh, cruel both with wrath and fierce anger, to lay the land desolate: and he shall destroy the sinners thereof out of it.
 10 For the stars of heaven and the constellations thereof shall not give their light: the sun shall be darkened in his going forth, and the moon shall not cause her light to shine.
(happens at the day of the LORD, at the time of his wrath)
 
Matthew 24:29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
(happens after the tribulation)
 
Joel 2:31 The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the LORD come.
Joel 3:15 The sun and the moon shall be darkened, and the stars shall withdraw their shining.
(happens at the second coming)
 
The 6th seal needs to happen at the very end
 
Parallel:
A problem with parallel are the ships in the sea.
Though, if parallel, the "2nd" trumpet & the "2nd" vial, appear to line up perfectly:
 
Revelation 8:8 And the second angel sounded, and as it were a great mountain burning with fire was cast into the sea: and the third part of the sea became blood;
 9 And the third part of the creatures which were in the sea, and had life, died; and the third part of the ships were destroyed.
 
Revelation 16:3 And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea.
Yet if both happen together, early on, then how can the following be?
 
Revelation 18:17 For in one hour so great riches is come to nought. And every shipmaster, and all the company in ships, and sailors, and as many as trade by sea, stood afar off,
 18 And cried when they saw the smoke of her burning, saying, What city is like unto this great city!
 19 And they cast dust on their heads, and cried, weeping and wailing, saying, Alas, alas, that great city, wherein were made rich all that had ships in the sea by reason of her costliness! for in one hour is she made desolate.
 
Telescopic:
(the old hand held telescope, you pull out a tube all the way, and another tube inside begins coming out)
(you pull that tube all the way out, and another tube begins coming out, etc.)
One way has the 7th seal be the 7 trumpets, with the 7th trumpet being the 7 vials.
This actually another variant of "series", which has the 6th seal way too early.
 
Another way has the trumpets & vials occurring during the 5th & 6th seal.
Also with the vials occurring during the 5th & 6th trumpet.
Also with the 7th seal, 7th trumpet & 7th vial simultaneous with the 2nd advent.
 
Combined:
Not everything is necessarily in linear, chronological order, series or parallel.
Some seals go with some trumpets & with some vials.
These groupings are not necessarily in order, or even one for one.
However they have similar things in common:
 
The 1st Seal, 5th trumpet & the 1st vial go together (see the file of that name):
They all have to do with the antichrist, the rider on the white horse, the king of the locusts being the angel of the bottomless pit, and the 1st vial being the sore upon those who had the mark of the beast & worshipped his image.
 
The 2nd seal, 2nd trumpet & 2nd vial all have do with blood, blood red
 
4th seal, 3rd trumpet, 3rd vial - two have to do with drinking deadly waters & death
 
3rd Seal, 4th trumpet & 5th vial have to do with darkness, black darkness
 
4th seal, 1st trumpet & 4th vial have to do with fire & hell
 
5th seal, 6th trumpet & 6th vial: two have to do with the altar, a different two have to do with the Euphrates, a different two have to do with the LORD's servants, and two have to do with those who refuse to repent.
 
6th seal, 7th trumpet & 7th vial have to do with great voices, earthquakes & the end.