Mkuu,
The questions you pose are many and difficult, difficult in the sense that they do no have easy answers, and that the answers given by many thoughtful people (even believers!) could be quite different
I want to approach these questions from a very general sense of God and morality in the Scriptures (the Old and New Testaments) In the Old Testament, the relationship of God with his people was deeply dependent on moral obligations - the commandments and the numerous ethical and moral requirements in Leviticus. If a person or group of people met a bad end, it was often because they had not obeyed God' law.
In the New Testament Jesus was frequently criticized and condemned by his religious leaders because he did not obey God's law. He ate with sinners and worked on the Sabbath, for example. Also it did not seem to matter to him whether those he helped believed in God. (the centurion, for example) And Paul made it clear that the Law no longer applied, because all were transformed in the risen Christ. In the New Testament, the expectations of the followers of Jesus are that they love God and love one another. But different moral systems flourished among them. The followers of Jesus in Jerusalem continued to follow Jewish moral prescriptions, but the followers of Jesus among the Gentiles did not.
Since the written scriptures are so rich and can give so many different messages about how God relates to his people, it is not surprising that Christians (or Muslims or Jews - also people of the Book) can have beliefs and express their beliefs in ways that vary quite considerably. I have lived and/or worked in 44 countries around the world and have been amazed and humbled by how differently Christians act on their faith in places as different as Japan, El Salvador, Jamaica, Germany, DRC, Mail, Uganda, Papua New Guinea Zimbabwe, and so on.
Can people develop ethical systems without reference to God? I think the great Catholic theologian Thomas Aquinas, tried to show that they can. If he was correct, then why can't you, as a non-believer, be a wonderful parent?
I happen to be a believer. I believe that God's grace is present to all of us, believers and non-believers alike. We respond to God's grace not necessarily by joining a church, but primarily by being as kind and loving to others as God is to us. God never gives up on us; that surely is the message in the parable of the prodigal son. The great job for Christians, I think, is not keeping count of their moral deeds, but rather witnessing to the loving presence of God that they see around them, even in places they never expected God to be.