While I have no trouble referring to the Bible as “God’s Word” it seems evident to me that when the New Testament refers to “the word” or “the word of God”, if it does not mean specifically Jesus Christ, the second person of the Holy Trinity, then it is referring to the good news of salvation preached by the church.
“Now these Jews (of Beroea) were more noble than those in Thessalonica, for they received the word with all eagerness, examining the scriptures daily to if these things were so.” Acts 17:11
“And we also thank God constantly for this, that when you received the word of God which you heard from us, you accepted it not as the word of men but as what it really is, the word of God, which is at work in you believers.” I Thess 2:13 I don’t think that what the Thessalonians received from Paul was a crate full of Bibles, as helpful as that might have been. They received the gospel. The letter to the Thessalonians is generally understood to be among the earliest written, or the earliest, of the books that now comprise the New Testament.
Yes, but the challenge the OP should posit to his Protestant relative is basically, “How do you know that the Bible is God’s word?” since the aforementioned Protestant came in with that assumption.
Catholics should not immediately admit that the Bible is God’s word when confronted by Protestants because it establishes the grounds for authority. Rather, they should throw back the question, e.g.
Protestant: Your practices are unbiblical!
Catholic: First of all why should we believe the Bible?
Protestant: Because it is the Word of God!
Catholic: Really? What is the basis for such a statement?
or
Catholic: What proof can you present for the Bible’s inspiration/authority?
Most likely the Protestant will quote 2 Tim 3:16 or some similar passage, but at this point, the Catholic has essentially gone into neutral ground by placing the burden of proof on the Protestant. Citing Scripture to prove Scripture is circular reasoning and has no validity in any argument.
So for the OP, do not agree yet that the Bible is God’s word. I know it, you know it, and we both know why we know it. But the Protestant expects us to swallow it on his own word.
It only shows how self-refuting Sola Scriptura is, because it cannot be proven from reason, only from assumption.