Thanks to Eric Marshall from Australia who discovered
the pair on the 1901 Census, it
turns out that Winifred and Kathleen Boxshall were the daughters of Frank Arkwell Boxshall and Annie Helena Chamberlain who married in 1891, the marriage being registered in Woolwich, London. In 1901 the family were living in Epsom, Surrey and in 1911 Kingston, Surrey.
Frank Arwell Boxshall was the son of Thomas Boxshall and Mary Ann Arkwell who married on 27 Nov 1860 in Lambeth, London.
Annie Helena was the daughter of John and Hannah Chamberlain and it was her sister Mary Ann Letitia Chamberlain who married Henry Thomas Weeks.
This makes the Boxshall sisters to be Helen Willliams (nee Lambert) first cousins twice removed.
Thank you Eric for inspiring this research. More details will appear on the website in due course but at least now we have one less mystery to solve!