That's the problem, you try to understand the scriptures naturally, but it's not a natural book ,it is to be spiritually discerned! Satan was given a offspring, a seed Gen 3:14-15! Also his offspring is not Gods Offspring! Two different o ffsprings !
That is right. One needs spiritual eyes to understand it. Allegory (your method) is an invention of man originating by a heretic, Origen. Even the RCC recognized this and excommunicated him. Augustine, one of the Father of the RCC, however, popularized this method of interpretation. It doesn't have much to stand upon. The early believers never used it. It is an invention of man. It does not use "spiritual eyes" but the eyes of the natural man.
The Bible was meant to be taken literally.
According to Genesis 3:15 the seed of the woman is Jesus Christ, a prophecy pointing directly to Him and no one else.
The offspring of Satan is totally spiritual, not physical.
An example of that is given in 1John 3:
1Jn 3:8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
--Whoever commits sin is of the devil, that is, whoever continues in a lifestyle of sin is of the devil.
In opposition to that John says:
1Jn 3:9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
--Those that are born again do not continue in sin because their lives have been changed by Christ. They have been born of the Spirit of God.
1Jn 3:10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
--Thus there are two: These are entirely spiritual--children of the devil and children of God. One becomes a child of God by trusting Christ.
1Jn 3:11 For this is the message that ye heard from the beginning, that we should love one another.
1Jn 3:12 Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous.
--The mark of a true believer is love.
The mark of the unsaved is selfishness. He looks out for #1--himself.
Cain did not love his brother. He murdered him. This was evidence that he was not saved; that he was "of the devil." It is spiritual not physical.