My suspicion is that Charles is the son of Robert Blake (father of Sacheverall baptized at Penton Mewsey) or Charles Blake who married Jane Frampton at Andover in 1683 although the time frame doesn't work quite as well. At the moment I do not have any children for the Charles Blake/Jane Frampton marriage so the Robert Blake line seems the more logical. There is a John Blake baptized 1714 at Penton Mewsey and the son of Robert Blake. He would be 82 in 1796 when John Blake died at Abbotts Ann if they are the same individual (John lived and married at Abbotts Ann but he was not baptized there as far as I can tell thus far). In that case the Charles Blake family (married to Jane Gilbert) would have been his great nephews. The will read like the relationship was that close. The relationship with my own line is still a mystery.
Thomas (my 3x great grandfather and mentioned in the will) Blake's grandfather Thomas King had left a bequest to the daughter of John Blake Malster so that the relationship could have been on the King side of the family rather than the Blake. It is a mystery! Every time I find new information it always provides at least one mystery or more which keeps one at genealogy for hours at a time trying to sort out the new mysteries.