About Mary Knowlys (Nelson)
A History of the Chief English Families Bearing the name of Knapp says
William Knowlys of London who was bur. at Bredfield. He m. 1750 at S. Sepulchre's London, Mary Porter of St. Andrew's, Holborn & left a son Thomas-John Knowlys of Fleetwood & Keysham Hall, Lanc., & Hill House, Windsor; b. 1803; m. 1822 Anna-Maria dau. of Robert Heksketh of Rossal.
However, it's unlikely that he could have had a child in 1803 with a woman who was of marrying age in 1750. Therefore, Thomas John Knowles must have been a son by a much younger wife or a grandson. The latter is assumed here until better sources can be found.