To take the last part first:
Your post is pretty ignorant and short sighted, based on a very narrow perception of the world you have. People like you really should refrain from having discussions about the metaphysical in AI when you clearly don't understand how humans have evolved in that respect, even over the past couple thousand years.
You shouldn't be quite so keen on putting down other commenters in this way - your own comments are not deeply insightful either, even you appear to think so yourself. All you achieve is to alienate the person you are talking to, as well as others who will see you as immature and lacking in self-confidence. And you don't actually need to try to put other people down - just keep to known facts, argue logically and accept that if you are wrong, you stand to gain new insight, so it is hardly a 'defeat'.
Plus, of course, where do you see that the GP 'clearly doesn't understand how humans have evolved'? To me this sounds like the kind of arguments I used to get into as a teenager who had just realised he knew it all - no more than agressive bluster, really. You'd do better by seeing the GP for what it most likely is: humour. Otherwise you'll end up sounding like a politician.
No, they won't. They will believe based on observations and known history. You do not know even how long you've existed. You believe you've existed your entire life, but your existence from your perspective is nothing more than a collection of memories that may or may not be real, you have absolutely no way to confirm or deny that, you can only assume that its true and move forward because assuming anything else is just a waste of time.
You are making some bold assumptions here; these are issues that have been discussed very throughly for centuries; summed up rather eloquently by Descartes: 'Cogito ergo sum'. The scientific method springs from the need to address the uncertainties of cognition being subjective - it is the best way we have been able to think of, which will over time help our knowledge progress towards objectivity, if applied scrupulously.
So, you assume that all intelligence must by necessity be like human intelligence; IOW, you haven't been able to imagine any other form of intelligence. I suppose most people have difficulty doing that - myself included - but that is no reason to assume that none exists. Apart from the fact that we don't really know what constitutes 'intelligence' and whether that has any bearing on things like consciousness and self-awareness, there are actually people to who not knowing everything objectively is not a burden, and to whom the idea of absolute certainty is seen as a threat; they are called scientists.