Regarding copying - try this thought experiment:

What if it were possible to probe a single neuron and copy its exact functioning - that is, the actual neuron and the artificial copy both act the same to the same inputs, and produce the same outputs. Not only that, but this artificial neuron, once fully copied and functioning, could then be inserted in parallel with the original. Then - kill the original.

So there's now this artificial neuron (it doesn't have to be inside the actual brain, either!) working exactly like the original. In fact, let's say this artificial neuron does exist outside the natural brain (and let's ignore any propagation delays or whatnot, though in reality, anything we did with electronics would be vastly faster than actual neuronal signal speeds).

So - we have "copied" (or "uploaded" if simulated with software) a neuron from the brain to a new place outside of that brain.

From the brain's perspective - everything is the same.

Do it over and over and over again - until all the neurons are copied from brain to outside of it.

Again - from the brain's perspective, everything is the same - but now it is completely artificial - and may even be running as a simulation in some fashion.

Now - we did this "one neuron at a time" - but how is that fundamentally different than if we could (somehow) make a copy "all at once in parallel" (something similar to the transporter of Star Trek) - then killed the original?

Of course - if that copy and the original existed and were aware at the same time - their experiences would diverge - but what if the copy was instead "wired" to the same inputs and such (that is, in parallel) to the original brain. In short, kinda like the original way we were copying and killing neurons, but this time, instead of killing the neurons (again, wired in parallel), we let them live, then killed them all at once at the end.

Since both sets are receiving the same inputs and producing the same outputs - where is the "being" or the "consciousness" at? Is it only in the natural brain - or in the artificial? Both at the same time? If we killed one, but not the other - where is the being now? Does it matter which we kill?

We could do the opposite - kill off one of the artificial neurons - and the being should still be ok, right? But what if we randomly selected which we killed - artificial one time, natural another - but since they are all wired together in the same manner and were operating in the same manner in parallel - now where is the "being"?

So - does it matter if we kill off the natural neurons in serial vs parallel? Furthermore, assuming everything is wired together in parallel - would copying everything, then killing off the natural side matter? At what point and "how" does the "being" transfer from one side to the other? Furthermore, how fast must the natural side be killed or shut off - and if there is a disconnect between the two sides - does that matter? Like - if the natural side is disconnected from the copy then a nanosecond later is killed - is the being now still in the artificial copy? What does the being experience in all of this?

The funny thing is - something like this already happens - naturally - to our bodies every day and over time. But we retain the concept of "self" and "being". But it happens slowly, and it doesn't happen "all at once" - a copy isn't made and then the original killed off, but rather cells die and are replaced (maybe not perfectly - leading to aging, disease, and possibly death) over the course of time - but by the above thought experiments - does that really matter, especially if it were done quick enough?

Like - imagine a single brain - but connected to two separate but identical bodies. When one blinks, the other blinks as well. Sever the connection with one of the bodies - the being in the brain should "go" with the body still connected, right? So if there are two brains, connected to the same body - and they are both operating in identical fashion - where is the being? Which brain? Both?

Again - this is all a thought experiment - which has been explored in depth by many people for quite a long while. It has been explored by science fiction several times. In both thought arenas, different conclusions have been made over what really happens - or might happen. But really, no one can say to know the answer.