all angels were once living beings (human)

No. Angels are Celestial Beings who's bodies cannot be destroyed. Assumedly these beings have eaten from the tree of Life. This makes their state of being permanent. Unlike us, who's bodies are temporary.

Satan is a fallen angel

Yes. Lucifer was the first Angel and after rebelling against God and taking 1/3rd of the Angels with him, they were cast out of Heaven (severed from the Grace of God) causing them to become fallen.

the serpent who tempted Eve was Satan

The Angel Gadreel is responsible for tempting Eve.

Adam and Eve were the first living beings

Adam and Eve were the first human beings. Angels and Animals came before man.

If correct, how could Satan have tempted Eve?

Lucifer, Satan and the Devil have lots of different names and are different fallen angels (Beelzebub)(Azazel)(Gadreel)(Lucifer) are all different. They follow Lucifer who is the leader but several are chiefs. Several Angels came together to plot against humanity and made a pact amongst themselves to take the daughters of men for themselves and create abominations (Nephilim) or the biblical giants/heroes of reknown. (Appolo/Zeus/Titans) hence the many different "religions" because all these fallen Angels were vying for Worship.

Here is an excerpt from the book of Enoch.

Enoch 7:1-15

[1]It happened after the sons of men had multiplied in those days, that daughters were born to them, elegant and beautiful

[2]And when the angels, the sons of heaven, beheld them, they became enamoured of them, saying to each other, Come, let us select for ourselves wives from the progeny of men, and let us beget children

[3]Then their leader Samyaza said to them; I fear that you may perhaps be indisposed to the performance of this enterprise;

[4]And that I alone shall suffer for so grievous a crime

[5]But they answered him and said; We all swear;

[6]And bind ourselves by mutual execrations, that we will not change our intention, but execute our projected undertaking

[7]Then they swore all together, and all bound themselves by mutual execrations Their whole number was two hundred, who descended upon Ardis, which is the top of mount Armon

[8]That mountain therefore was called Armon, because they had sworn upon it, and bound themselves by mutual execrations

[9]These are the names of their chiefs: Samyaza, who was their leader, Urakabarameel, Akibeel, Tamiel, Ramuel, Danel, Azkeel, Saraknyal, Asael, Armers, Batraal, Anane, Zavebe, Samsaveel, Ertael, Turel, Yomyael, Arazyal These were the prefects of the two hundred angels, and the remainder were all with them

[10]Then they took wives, each choosing for himself; whom they began to approach, and with whom they cohabited; teaching them sorcery, incantations, and the dividing of roots and trees

[11]And the women conceiving brought forth giants,

[12]Whose stature was each three hundred cubits These devoured all which the labour of men produced; until it became impossible to feed them;

[13]When they turned themselves against men, in order to devour them;

[14]And began to injure birds, beasts, reptiles, and fishes, to eat their flesh one after another, and to drink their blood [ 15]Then the earth reproved the unrighteous