How about Charles lives here, or the room of Charles saves a lot of bother. However the correct way is Charles's room Just as you would say e.g. Jack's room
I always was taught that if the name (ie Charles) ended in an *s* then you did not add the extra *s*, if it ended in any other letter, then you did add the apostrophe and final *s*
There is no right answer. You will churches called St Thomas's and others called St Thomas'. Many argue for Charles' but I prefer Charles's on the basis that this is how it is spoken aloud.
LOL I think certain rules must have changed over the past few years.... one of my colleagues decided that a report written by a member of his staff was gramatically incorrect because they had written *its* to mean the possesive pronoun of *it*... He declared that it should be *it's* because if you write the possessive of *Jack* it is *Jack's*.... When I saw said report the errors leaped out into my face but he swore black and blue that he was right... until I showed him the relevant page of the Concise Oxford Dictionary.....
When I was at Cambridge we had our names on our doors, and it just said "Bertie" or "Gerald" or "Potter Minor" no controversial stuff with apostrophes. So your answer is "Charles". Don't get tied up in grammatical details.
The BBC TV programme 'Balderdash and Piffle' always contains a round where the teams have to provide the correct punctuation. In almost every programme they have to point out that while the form <Charles' room> is frequently used (and, indeed, is widely accepted) it is most definitely wrong. The correct punctuation is <Charles's room>.
Both 1 and 2 are perfectly correct. Even when there are threes sounds involved, it is still OK to include them all, though the final one is often dropped. For example, one can write about Jesus' crucifixion or Jesus's crucifixion. With only two letters s involved, you can, for example, write about Keats' poems or Keats's poems.
In the Charles case, exactly the same applies.
I should perhaps have added above that Sir Ernest Gowers, regarded as an authority on English usage, in his Plain Words, opens the section on apostrophes in names ending in s with the words...
"There is no universally accepted code of rules governing the formation of the possessive case of names ending in s."
He goes on to illustrate the point. From the horse's mouth!