It is certain in the Acts passage and quite likely in the Peter passage that these were not Christians, or at the very best (In Peter) immature Christians, "untaught and unstable". By contrast, John "You need not that any man teach you, etc."
The point is that, ultimately, scripture and the God who unlocks Scripture, is our infallible source of guidance.
I do like how you use Scripture to make your points, even flawed points, it shows the practice of Sola Scripture, which you say is phony.
Two questions for you;
1) Can a person be taught by God and saved through reading the Scripture alone?
2) Can a person be taught by God how to love God and love their neighbor through reading the Scripture alone?
Yes they can, .... lets modify your questions:
"1) Can a person be taught by God and saved through reading the Coca Cola nutritional facts alone?
2) Can a person be taught by God how to love God and love their neighbor through watching STAR WARS THE LAST JEDI?"
The answer would be YES. With God nothing is impossible.
You have deceptively worded your question to where obviously a person could only say yes.
Scripture ALONE however does not work.
Lets just put you the new christian with a bible written in Greek or Chinese, and nothing else at all.
You need multiple authorities to guide you.
No one reads the gospels and remains clueless of the life of Jesus, no one concludes things like faith alone by themselves, without extra help and a twisted emphasis on epistles.
Finally SCRIPTURE ITSELF doesn't point to itself as the FINAL and ONLY authority.
It does however multiple times POINT TO THE CHURCH.
Jesus Christ points to the church.
The Church is ONE FLESH with Jesus Christ.
The Church is GOD BREATHED.
Scripture is NOT ONE FLESH with Jesus Christ.
Scripture is NOT the bride of Jesus Christ.
Scripture is NOT the PILLAR and Foundation of Truth.
Scripture is NOT the Body of Christ.
Ephesians 1
15For this reason I too, having heard of the faith in the Lord Jesus which exists among you and your love for all the saints, 16do not cease giving thanks for you, while making mention of you in my prayers; 17that the God of our Lord Jesus Christ, the Father of glory, may give to you a spirit of wisdom and of revelation in the knowledge of Him. 18I pray that the eyes of your heart may be enlightened, so that you will know what is the hope of His calling, what are the riches of the glory of His inheritance in the saints, 19and what is the surpassing greatness of His power toward us who believe. These are in accordance with the working of the strength of His might 20which He brought about in Christ, when He raised Him from the dead and seated Him at His right hand in the heavenly places, 21far above all rule and authority and power and dominion, and every name that is named, not only in this age but also in the one to come. 22And He put all things in subjection under His feet, and gave Him as head over all things to the church, 23which is His body, the fullness of Him who fills all in all.
If the CHURCH is not your authority You are stating Jesus Christ is NOT your authority, they are ONE.
IF you don't think the Catholic Church is the Church, I call that a Valid argument. <-thats fine, even NOBLE if you following good conscience, aka not lying to yourself, or cowering behind peer pressure.
IF you don't think the Church,(actual church as you believe) is not the highest authority, I call that a IGNORANT argument.
Those who oppose the Church oppose Jesus Christ. The only way the church can say anything at all is when the head of the church, JESUS CHRIST has spoken.
Jesus Christ is the absolute BOSS of the Church.