1. I don’t like to use the word “objective.” It’s not a Biblical word. I also find the word “known” problematic. Without knowing how you mean “know,” I wouldn’t know how to answer. I believe people are saved not by objective truth, but by Jesus. Their faith isn’t in their knowledge, but in God. I believe the Bible can make us wise to salvation. I hope that helps!
2.Do you mean the Bible without the guidance of the Holy Spirit? The Bible tells me that the Holy Spirit guides us into truth, so I would feel uncomfortable crediting the Bible with guiding us into truth to the exclusion of the Holy Spirit, since the Bible itself tells me this.
3. Yes. I also believe that born again Christians can be wrong, so their confidence should not be in their certainty, but in the grace of God