This is a complicated family with little information. I have the 1901 census with the 3 children - Alfred is my grandfather, but became estranged from the family and by the 40s, disappeared off the scene altogether. Piecing together scraps of family stories has helped a little bit. Violet was always referred to as his half sister. I found Violet and Alfred as schoolchildren boarding with different families in Newbury, Berks in 1911, but cannot find Ann Campbell, who may have remarried, or have been in an institution. The 1901 address became a business property, so is not listed at all for 1911. I could not find the sibling John in 1911 so he may have died or been transported, or, as is the danger with all the digitised records, been transcribed wrongly. I did find a John of the correct age in the 1911 census, but when I went to the original records, the age had been copied incorrectly. My mother has never heard any reference to this brother either.
What we do know is that Ann Campbell at some point fell down some stairs and then lived in an asylum, so I assume that she was mentally or physically incapacitated or both. No idea when this happened, although my grandfather did visit her in the late 20s. Of course, inmates were often only listed by initial so it's difficult to find her or her death. She may have had the accident before 1911, which would explain why the children were boarded out and attending school in another town. But why Newbury? No idea.
Going back to the 1901 census, all 3 children were show as born in Pancras, London, but in fact John was born in Bloomsbury - I have his birth certificate. Violet was born in Pancras in 1900 - I have her birth certificate too. The Govt Records Office cannot find a birth cert for Alfred for Pancras or West London generally.
The mystery is Alfred's parents - presumably Ann nee Crook and AN Other. On Alfred's marriage cert, he states that his father is 'a gentleman, deceased' which does not fit with a commercial traveller, deceased! Fantasy or fact? There was also a family story that his father was a doctor, but whether a medical or clerical one, or an exaggeration (perhaps some medical connection?) we don't know. I could not find Ann Crook in the 1891 census, but did find Ann Croak (who I think is Crook - the handwriting is shaky) visiting a family in Harley St, that made me think that the mystery father might have had Harley St connections, and someone somewhere has surmised, rightly or wrongly, that he was therefore a doctor.
I thought that the parish records themselves, rather than digitised online records, might shed some light on Ann Crook, possibly marrying another rather than John Campbell.