There are a number of different aspects intertwined in your question and I cannot answer all of those aspects together, but I hope that by making one point clear that it will make others clear also.
Green’s Interlinear Hebrew and Young’s Literal translation agree on the English translation of the Masoretic text of Genesis 3:15 (Young always uses a present tense as a literality) :
And enmity will I set/I set between you and the woman, and between your seed and her seed
He will/doth bruise you the head. And you shall/dost bruise him the heel.
‘Seed’ here is singular. Paul points out that ‘seed’ can be singular in Galatians 3:16 :
Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.
So also in Genesis is it said by God to the Serpent of the future seed of the woman :
He (singular) shall bruise thy head. And thou shalt bruise his heel.
Here, a rearrangement is prophesied by God. For mankind had fallen under the Serpent by transgression. The Serpent had gained control by deceiving the woman, who in turn caused the man to transgress and they both had fallen under the power of the Serpent. Cast out of Eden they were to till the cursed ground until they died and were buried in it.
But in the promised rearrangement, the seed (singular) would be above the Serpent. From above, he would bruise the head. Retaliating, the Serpent would only be able to bruise the heel of the one above him.
Then how the rearrangement ?
In subsequent prophecies, more would be revealed. But for the time being that was all that was revealed to Adam and to Eve (and to the Serpent). But it was enough for Adam to name his wife - Eve, in recognition that she would be the mother of all living. That is, all who truly live.
She would also be the mother of all the seed of Adam, but that is a different matter.
From Eve there was promised, by God himself, a seed (singular) through whom would be a rearrangement that would overcome all that had transpired in Eden. That which the Serpent had done, that which the woman had done and that which Adam had done - all would be resolved by the coming seed.
Just how that seed would come - and just how that rearrangement would be accomplished - are made clearer in subsequent revelations from God. It was not yet revealed how a seed would come who would not be subject to the consequences of Eden. How could it be possible ? was a question that could not - then - be answered.
I hope that this clarifies just one aspect of the research in which you are engaged.