By the way, the JW belief about Jesus being the firstborn is entirely incorrect. As far as Michael the Archangel is concerned, I think they may have a point there. I did check the verses but still undecided.
Let's look at the first argument. There are 3 meanings to the term "Firstborn".
Firstborn has 3 meaning:
1 First born child ( chronological order)
2. Heir
3. The one who is Preeminence (supremacy)
In the Torah, it is said that if a man has 2 wives, one he loves and the other he hates (or loved less), he should not give his inheritance to the son of the second wife whom he love more just because he love the first wife less. The firstborn gets a double portion of his father inheritance and the rest is split among the other sons.
Deu 21:15 If a man has two wives, and he loves one but not the other, and both bear him sons but the firstborn is the son of the wife he does not love,
Deu 21:16 when he wills his property to his sons, he must not give the rights of the firstborn to the son of the wife he loves in preference to his actual firstborn, the son of the wife he does not love.
Deu 21:17 He must acknowledge the son of his unloved wife as the firstborn by giving him a double share of all he has. That son is the first sign of his father's strength. The right of the firstborn belongs to him.
Let's look at the story of Abraham. Abraham has two wives. Sarah and Rachel. Ishmael is Abraham's firstborn son through Rachel. His second born was Isaac through Sarah. Remember Sarah couldn't bear a child so Abraham took Rachel as his second wife? Well according to the Torah, Ishmael was supposed to be the one to receive his father inheritance. Guess what? He didn't even though Ishmael was firstborn (chronologicall y) it was Isaac that became the firstborn (heir and supremacy/status). God's covenant and promise was with Isaac.
Let's look at a second example. Remember the story of Joseph whom his 11 brothers rejected him and sold him into slavery and he ended up in Egypt? Joseph's father is Jacob who begot 12 sons. Reuben is the firstborn son and Joseph is the 11th son. If you understood the story Reuben slept with his father's maidservant and dishonor him. By committing a great sin his birthright was removed and was given to Joseph.
1Ch 5:1 The sons of Reuben the firstborn of Israel (he was the firstborn, but when he defiled his father's marriage bed, his rights as firstborn were given to the sons of Joseph son of Israel; so he could not be listed in the genealogical record in accordance with his birthright,
1Ch 5:2 and though Judah was the strongest of his brothers and a ruler came from him, the rights of the firstborn belonged to Joseph)--
1Ch 5:3 the sons of Reuben the firstborn of Israel: Hanoch, Pallu, Hezron and Carmi.
Do you see now that "firstborn" does not always refers to a direct son?
King David was also God's firstborn even though he isn't the firstborn chronologicall y. He is the 8th son born to Jessi. King David wasn't the first king as well. Because King Saul was a king of Israel before David.
Psa 89:19 Once you spoke in a vision, to your faithful people you said: I have bestowed strength on a warrior; I have exalted a young man from among the people.
Psa 89:20 I have found David my servant; with my sacred oil I have anointed him.
Psa 89:26 He will call out to me, 'You are my Father, my God, the Rock my Saviour.'
Psa 89 :27 I will also appoint him my firstborn, the most exalted of the kings of the earth.
When the Bible talks about Jesus being the firstborn of all creation, it means that Jesus is the heir and have supremacy over all creation. He is not a first born in the chronological sense. Jesus is not a created creature. Even though some people in Bible may be firstborn chronologicall y, God could reverse this order around.