Yes. All we do is dictated by sensations, as you put it. Even the feeling of knowing what is true, is just a sensation, an appearance in your consciousness.
But how would this be any different for a Christian? Your brain probably works the same way mine does.
Because we can pretty reliably say that it's better to be kind than to steal. When we treat others badly, it's usually because we lack knowledge. The more you know about another person, the more you'll realise that he's the same as you, with all the emotions and needs and rights etc that entails.
Yes, but the sensations in their brains didn't come from nowhere. They have causes. If we examine the causes they quickly become far too intricate for us to really know, because everything is interconnected. Upbringing, society, hormones, movies, you name it. It all shapes who we are and what we do.
You may rightly claim that unless God put down the rules, there's no
objective standard of morality. That may be true, but that doesn't mean I must believe in God to have morality. I couldn't get rid of my morality if I tried. There's no escaping it, and it doesn't depend on believing in God. So morality is one thing you would certainly not lose if Christianity turns out not to be true.
I wish I knew
Consciousness is probably the greatest mystery there is, and it wouldn't surprise me if it's fundamentally impossible to figure out exactly what it is and what it's for. There's the idea of panpsychism, which sounds like mumbo jumbo but may actually turn out to be true. It says that consciousness is a fundamental quality of matter, like charge and spin. It would mean that the tiniest particle has some sort of consciousness, though probably nothing like the human mind - no memory or emotion or sense of self, but still some extremely basic form of awareness. I know, it sounds mumbo jumbo, but if you think it's interesting, look up the philosopher David Chalmers.
But I guess you would think that consciousness itself is a good argument for God, and I think I agree with that (it could point toward some deity or "purpose", but not Jahve in particular).