As an Australian I would say everything the same way as the American except the last one where I'd say 'Elijah is back from London already'.

Yes. And no. And sometimes. Yes, British people say all of those things in your list under 'British'. But no, it is not quite that simple. In fact, many people also say the things in your list under 'American'. Some people in Britain use both. They all sound reasonably natural to the British ear, and nobody would think it the slightest bit strange if I were to say 'Let's take a break' or 'I'm going to take a shower'. Many younger British people might even think that the so-called American expressions sound more natural, and use them in preference to the supposed British ones. The fact is that there is NO great divide between the variants of English. It is impossible, and a waste of time, to try to draw a clear-cut line between British and American English. The differences, such as they are, are not black and white. The overlaps are many and complex and - most importantly - changing all the time.

Hi, I can only speak for the American expressions. These are all correct, except for the last one. Americans would say either "Elijah has already returned from London", or perhaps more commonly, "Elijah is already back from London."