2-Is it true that the Bible or at least some passages of the Bible can be used to harm people?
3-Is there any position (kneeling, standing and so on.) that pleases God more when we pray or are there objects that we can associate to our prayers (candles, ash etc.). that will help them to be heard and granted?
Yes, God does respond to the prayers of unbelievers. Of course, that depends on what you mean by an unbeliever. By one definition, anyone who prays to God is a believer!!!. Let me change your question. Perhaps what you are asking is whether God hears the prayers of those who are not yet saved. Some use passages such as John 9:31 to show that God does not hear the prayers of sinners. We should be very cautious in taking this statement as doctrine, because it is coming from a man who was not even a follower of Jesus, whose statement does not have any authority. Others use Isaiah 59:1-2 which says that our sins hinder God from hearing our prayers. Now, I do believe that our sins do hurt our relationship with God. I also believe that those who are saved by the blood of Jesus–who have received the indwelling gift of the Holy Spirit–do have an especially close relationship with God. The Holy Spirit intervenes for Christians in their prayers (Romans 8:26-27). However, it is obvious from what we know of God and from examples in scripture, that God does hear the prayers of those who are not yet saved and that he will respond to their prayers. God heard the prayers of Cornelilus (Acts 10:1-3).
Of course, people can use the Bible to hurt people. All kinds of wicked people have abused the Bible to justify their own sinful behavior. I am sure that even sincere Christians (including myself) use the Bible incorrectly at times, bringing harm on themselves and others. The Bible, legitimately used, will not harm anyone, but you are well aware that many use it in ways God would not support. People have used the Bible to justify slavery, abuse of women by men, making people feel guilty even though they are forgiven and many other things.
No, there is no position which is more pleasing to God than another. There is no passage in the New Testament which says one prayer position is more spiritual than another. Paul urges people to "lift holy hands in prayer." There is some evidence of people praying on their knees in the New Testament, but there is no indication in the scripture that one position is better than another. Similarly, God does not need prayers, icons, statues, incense or anything else in order to hear our prayers. Such props very from idolatry to harmless helps to prayer. If a candle or kneeling in a particular position, or walking, or looking at the stars helps someone to focus on God, so much the better. That is an individual thing, but there is no position or object which changes how God hears us.