Collins had gradually brought his sons into the business. Drawings began to be signed Collins and Sons. Herbert Collins set up Herbert and Company; Billy later set up his own company to complete Rookfield Estate, while Ralph had his own building firm.
The drawing of the large house at the corner of Fords Green and Fortismere Avenue, dated 1908, is signed W.J.C & Sons and J.D.R.Mouro. It is a fine building in roughcast, with hanging tiles, square corner windows on brackets, a huge roof in rich hand-made tiles and tall chimneys. One could be in Letchworth, or Welwyn Garden City, or in large grounds in Buckinghamshire.
When Birchwood and Leaside Avenues had been completed, Fortismere House was demolished and the whole family moved to Rookfield, the large house on the Rookfield Estate, halfway down Muswell Hill, where they continued to live as they had lived in Fortismere House, but this time with the Rookfield Estate houses rising around them.