Badcock and Seaby mystery

Well, another contact through myroots has revealed another family history mystery. My great-grandmother Lavinia Seaby had a younger sister, Margaret Jane, who was born in 1869 in Dry Drayton, Cambridgeshire. Margaret appears as a one-year old in the 1871 census with her parents William and Emma Seaby and siblings Samuel, Lavinia, Phillis, Lucy and Solomon. Margaret and Solomon are still at home with their mother Emma and her new (as yet undeclared) husband Jonathan Treaviss in the 1881 census. By 1891, Margaret has married a William Badcock (married in late 1887, Cambridge district) and is living with him in a caravan "situated in the yard of 'The Bottle House', Swavesey, near Fen Drayton with a one year old son, William Badcock.

Margaret's husband appears to be the same William Badcock born in 1836, Dry Drayton, her mother Emma's brother.  Margaret went on to have at least three more children, although it isn't clear whether William Badcock is their father or not.  By 1901, Margaret is living with her widowed mother Emma Traviss, and four children: William (now aged 11), Lucy (9), Ernest (7) and Kate (1). 

My latest myroots contact is descended directly from Margaret's son William, who by 1901 was using his mother's surname Seaby, like his brother and sisters.  Interestingly, his brother Ernest was registered with the middle name Cook - perhaps an indication of his father's surname (although I haven't looked at his birth certificate to see if a father is mentioned). 

William Badcock senior isn't readily visible in the 1901 census, but his death is also not readily found in the BMD indices. Was their marriage annulled after their relationship was discovered? Was William really the father of his niece's children (or some of them?). He had no children with his first wife of some thirty years, Mary Ann (nee Papworth); they were married in 1856 and Mary Ann was buried in September 1887, a short time before her widower married Margaret. Although I haven't seen the original source or a transcript, Mary Ann's burial was apparently 'on Coroner's order' ... perhaps the local newspapers could reveal why.

The story is a fascinating one and leaves many tantalising questions to be answered.  FreeBMD has two marriage entries for a Margaret Jane Seaby - one in 1887, the other in 1904.  Did she marry again? Perhaps the 1911 census, once released, might give us a clue.