Question

if there are 2 electrons in the 1S orbital and 2 in the 2S orbital, are these 4 electrons in the same space or is the 1S orbital in a completely different space as the 2S orbital?

Answer 1

That is a very good question, I don't seem to remember QM much but here is my attempt :
Below waveforms show the "radial probability distribution", finding the electron at a distnace "r" from the nucleus. Notice that the electron in 1S orbital can be anywhere, but there is one most probable radius. Also the electron in 2S orbital can be anywhere except at one radius(node, where the radial probability is 0). So the space is not exclusive, 1S and 2S electrons share the space, but each can be found most of the time at their most probable radius...