Hello, I don't know where you are in your search for Eltham-Harrison relatives, but as the grandson of Charles Eltham Harrison, born May 1881, Hamilton, Ontario, I can confirm that most of your information regarding the Elthams of Berkshire appears to be quite accurate. Edward Harrison (born Edward Eltham) is the only child of John and Ann who changed his surname after emigrating and no one was ever able to clarify why.
I was only 13 when my grandfather died in 1963 and I guess I wasn't curious enough to ask him if he knew why great grandfather Edward changed his name to Harrison. However, I know my father, Charles Grayson Harrison would have found out at some point in his life as he was always interested in family history and he couldn't tell me why any time I asked him before he died in 2015.
Seems strange that no one would know why.
I had certainly heard from my father about Grandad's half brother who had emigrated from Ontario to Texas.
My grandfather Charles used Eltham as a middle name as did his son, Hugh Eltham Harrison. I am not aware of any current usage of the name Eltham amongst the children of my nieces, nephews or indeed cousins and their offspring.
My father, Charles Gryson Harrison was the only child of Charles Eltham Harrison and Alice May Peebles, the younger sister of Bessie Peebles mother of the C E. Harrison's first four children - Mary-Louise, Hugh, Elizabeth, and Edward. Bessie died of complications following childbirth and Alice May moved in to care for the children. Some years later, Charles realized he had become smitten by Alice May and they were married. She later gave birth to my father who was significantly more than a half brother, as his mother's DNA would be pretty much identical to her older sister.
If there's anything I can help you with, please don't hesitate to ask.
Sincerely,
Hugh Clinton Harrison,
born Hamilton, Ontario, Jan 2, 1951
to Charles Grayson Harrison (1924-2015) and Nancy Alice née Wigle (1925, still alive and well and living at home at 97)