I have not mastered those books or fully understand them, I only started reading and going over many of them several months ago. I don't understand greek or hebrew, though would love to learn them, but I don't think there is time for that.
You can get online translations and interlinear versions of those books, as well as several ancient hebrew/greek biblical documents. You can read the english translations, then how the 'said' book or translatation would rephrase them and compare to various bibles.
Book of Jasher for example, talking about Cain murdering Abel, you read..... "7 And in some time after, Cain and Abel his brother, went one day into the field to do their work; and they were both in the field, Cain tilling and ploughing his ground, and Abel feeding his flock; and the flock passed that part which Cain had ploughed in the ground, and it sorely grieved Cain on this account.
18 And Cain approached his brother Abel in anger, and he said unto him, What is there between me and thee, that thou comest to dwell and bring thy flock to feed in my land?
19 And Abel answered his brother Cain and said unto him, What is there between me and thee, that thou shalt eat the flesh of my flock and clothe thyself with their wool?
20 And now therefore, put off the wool of my sheep with which thou hast clothed thyself, and recompense me for their fruit and flesh which thou hast eaten, and when thou shalt have done this, I will then go from thy land as thou hast said?
21 And Cain said to his brother Abel, Surely if I slay thee this day, who will require thy blood from me?
22 And Abel answered Cain, saying, Surely God who has made us in the earth, he will avenge my cause, and he will require my blood from thee shouldst thou slay me, for the Lord is the judge and arbiter, and it is he who will requite man according to his evil, and the wicked man according to the wickedness that he may do upon earth.
23 And now, if thou shouldst slay me here, surely God knoweth thy secret views, and will judge thee for the evil which thou didst declare to do unto me this day.
24 And when Cain heard the words which Abel his brother had spoken, behold the anger of Cain was kindled against his brother Abel for declaring this thing.
25 And Cain hastened and rose up, and took the iron part of his ploughing instrument, with which he suddenly smote his brother and he slew him, and Cain spilt the blood of his brother Abel upon the earth, and the blood of Abel streamed upon the earth before the flock.
26 And after this Cain repented having slain his brother, and he was sadly grieved, and he wept over him and it vexed him exceedingly.
27 And Cain rose up and dug a hole in the field, wherein he put his brother's body, and he turned the dust over it."
Does it not appear to go perfectly in harmony with the bible, and give a better understanding. THEN in the bible we hear how Lamech had killed a man and if cain was to be avenged, then Lamech 77 times. But who did he kill? Well in Jasher it says....
(I'll let you read it or look up yourself, but that Lamech accidentally killed cain in a hunting accident)
again seems to go perfectly in harmony with the bible, then it goes on to show how Enoch became very wise and people all over the world went to him for wisdom and understanding. Then it never mentions about angels coming to earth, but that man became very wicked and the flood was due to man.
So in the beginning, book of Jasher teaches man became wicked, and God taught Enoch what to teach mankind, and knowledge.
The book of Jubilees shows that 'watchers', angels involved directly with earth came to earth and defiled themselves. first there was a flood of eden, then the great flood. that watchers (I think that they were told to teach people how to serve god and taught many things, then defiled themselves while on earth)
In the book of enoch, shows how a bunch of rebellious angels made a pact to go to earth, and when there taught sorcery, forbidden things, and had relations with humans. Then they even went to enoch to talk to God on their behalf since he was righteous in Gods eyes. THere was a flooding of cains land when rivers surrounding it flooded. But then the great flood later on.
The "bible" we have, shows that the angels materialized and had relations with humans. Enoch was a rightous person but not details, then flood came.
Many of these other books give details where they are lacking in the bible. What is very much of note in the bible, is you will see how Cain and Seth, their children had very similiar or identical names. Cain's first son was Enoch, and down the line you had from Seth Enoch, who followed God. Cain's son Enoch became of a great nation. In the bible, see how similar so many of the names are, which could be used to deceive and give alternate or counterfeit truths.
It's AMAZING how trying to find a fault in one can be difficult, and how perfect and cover every chance is covered. For example, in the bible we have the years lived by the men. In what I thought could have been a counterfeit, the bible shows that Noahs grandfather died the same year of the flood, and in one of these books shows how he was a true servant of Jehovah, so I thought, AHAHA, now I'll catch a lie, lets see it explained how he died if he was a true servant of God. Well the book that talked about that, mentioned that Jehovah had waited until he died to begin the flood. Okay, so I 'guess' that could be true, it addressed it. That's as much as I will talk about, as I am not giving away anything, but hoping it gets you thinking. Beyond this would only be a one on one basis or with those I know are really seeking the truth and to serve God. At the very least, many other sources can give further insight on teachings. In James he talked about the prophecies of Enoch. Also apostle paul spoke about the 3rd heaven, being paradise or looking like it. (there is an ancient document and verified, which gives insight into what exactly he may have been referring to)
Even though you may have seen untruth, don't forget that the falseness and lies are based on what you were taught scriptures meant. If you allow God and trust in him, you may find much truth, and what you thought were lies can melt away.
I'll leave this at that. I'm not looking for anything, only to give the little push of encouragement that may have been needed for the sheeplike ones to maybe reinvestigate their final conclusions and perhaps go over more then they had before.