So I know you write Charles' instead of Charles's but how do you say it?

[cleanandclothed]

I presumed you still say Charles's. But Steven Fry reading Harry Potter pronounces Sirius' as Sirius not Sirius's. What is right?

I would trust Steven Fry!

I think it sounds like Charleziz. But I would also say Siriusiz, so what do I know?

In 'eats shoots and leaves' it says you should use what sounds better, what makes the sentence flow. It is the meaning that is being conveyed that is important rather than what is correct according to the rules. It says that it is a bit ridiculous to insist on James' pencil case rather than James's pencil case.

Oh good, I'll go with eats shoots and leaves then. I had never even considered that you wouldn't add the 'ziz' however you write it.

Tbh these days (and I am a pedant) I write it how it is said, so Charlesiz would be Charles's or Jamesiz would be James's.