Francis’ sister Mary (1682) married William Walter 13 May 1706. They had at least three children at Lyndon. One of these was Elizabeth, baptized 26 May 1708 and she married John Palmer at Lyndon in 1744 (exact date unclear).
They had two sons John (24 Jan 1745) and William (11 Jun 1749). These two are grand nephews of Francis and therefore undoubtedly the two referred to in the will.
BT of registers attached. The page for John also includes the burial of Francis Shelacres and the baptism of Thomas Walter, a grandson of Mary Shelacres (1682).