I am not much help as I can only go on one example but it seems like there is something going on. DS 4 also started reading at 2 - whole words only, photographic memory. He used to guess words based on the beginning and ending and couldn't sound them out at all... In contrast the phonics and sounding out have come this year without any teaching. He occasionally mixes the letters around with writing and doesn't always notice. Also the fact that Aidrn's brother is catching up suggests that there could be an issue also. No idea what the issue is though. Makes it difficult if no-one will look into it because of his age. I hope there are more helpful answers for you!
