Thank you for your replies.
Interesting idea that Walter may have been brought up outside the family, avm228. It is certainly odd that he is the only one who is not at home in 1891. Maybe he was a difficult child! The father, Edwin, died in Hastings, Sussex from pernicious aneamia and it has 1 1/2 years in brackets. Edwin's brother was present at the death and is the informant. I'm not sure why he'd returned to Hastings, maybe just for a visit.
Yes, Paul, you're spot on - Edwin Dunk and Emily Rosier are the parents, and that is them marrying at St John's Church. Thanks for the link to the website as I'd not seen it before.
And re: Hilda Emily Margaret Dunk, she is the daughter of Ernest, who was Edwin and Emily's 4th son. Fancy that! I have her marrying Victor Alexander Waldeck in 1933, but no record of any children.