Samuel FitzRandolph Jr. (b. 1694, Woodbridge, New Jersey) presumably had a bunch of children before son Benjamin FitzRandolph (born 1737), by both a first wife Frances (married by 1719) and second wife Johanna Kinsey (married in 1729). However, the only known (presumed) child born before 1737, would be a daughter Margaret FitzRandolph (b. ca. 1727-1732).
Margaret FitzRandolph was married in 1750 to William Waller. and William Waller was employed by Samuel FitzRandolph Jr. shortly after that marriage (on Samuel's ship that would be involved in an act of piracy). It doesn't prove a "father-in-law/son-in-law" relationship, but it seems very likely. Whether Margaret was a daughter of the first wife Frances or the second wife Johanna is still uncertain. But the question is how many children Samuel FitzRandolph Jr. had with his first wife Frances between 1719 and 1729 (and perhaps even earlier). It is a void that cries out for missing children, likely including Margaret (FitzRandolph) Waller.