Hey its a mcfly fan! lol welcome!
ive just finished The Last Battle literally 10 mins ago! I found it really hard. Basically (beware spoiler coming up) the Narnia in all the stories isnt really Narnia. Its like a copy of the real Narnia. And when people die in the fake Narnia, they go to the real Narnia. And its the same for all the worlds. So the England we're in is actually a copy of the real England and when we die we go to the real one. So when the fake Narnia "dies" everyone gets taken to the real Narnia and all the people or creatures from the other Narnia books who have died, are there. Tumnus, Mr and Mrs Beaver, Prince Cor and Corin, King ? (i cant remember what the first King was called) and Queen Helen etc etc And also from the real Narnia, you can see the real England and they join, so because Lucy, Professor Kirke, Lady Polly, Edmund and Peter died in the train crash, they are also there, but they got pulled away by magic to Narnia right before the train crash so they dont know about the copy of the worlds. So right at the end they Edmund, Peter and Lucy see they're parents on the real England coz they were in the train when it crashed. So now all the humans are dead on the Copy of England so they stay in the real Narnia and the real England etc etc But Susan is still in the fake England coz she wasnt on the train so you never know if she gets back to Narnia with the tohers or if she stays in England till she dies.