I have been researching Touzeau from Guernsey for many years. Some information on your Touzeau descendancy:
Your gggrandparents, Stephen Martin and Elizabeth Touzeau married, presumably in Guernsey, on 29 May 1817.
Elizabeth Touzeau was born on 4 Apr 1793 in St Peter Port, Guernsey, baptized 7 April 1793 in the Town Church, was the daughter of Roland Touzeau and Elizabeth Tosdevin who married on 27 Sep 1791 in Guernsey.
Roland Touzeau born 7 Aug 1766, baptized 13 Aug 1766 in St Peter Port was the son of Jacques Touzeau and Jeanne Touzeau (first cousins), he died 5 Jan 1817.
Jacques Touzeau born 1 Jun 1743, baptized 3 Jun 1743 in St Peter Port was the son of Jacques Touzeau and Marie Green.
Jeanne Touzeau born c1743 (presumed Deptford, Kent) was the daughter of Roland Touzeau and Marguerite de Grave.
Jacques Touzeau born 6 Jul 1715, baptized 9 Jul 1715 in the Town Church, St Peter Port was the son of Jean Touzeau and Marie Baudry. Jacques and Marie Green were married on 14 Sep 1740 in the Town Church - 7 children were recorded for them in the Guernsey parish registers.
Roland Touzeau born 26 May 1708, baptized 6 Jun 1708 St Peter Port, was the son of Jean Touzeau and Marie Baudry. He was married on 11 Mar 1739 at Glasshouse Street and Leicester Fields Huguenot Church, Westminster, London, to Marie Marguerite de Grave (daughter of Jaques de Grave and Anne Marie Veugny). Information from their wills shows that he was a hatter in Deptford, Kent and that they had three daughters and a son:
1) Jeanne - who married her first cousin, Jacques Touzeau (thought to have come to London to be apprenticed to his uncle, Roland), died 10 Jan 1786 St Peter Port.
2) Ann - baptized at St Nicholas, Deptfort, Kent 28 Aug 1744 married there on 29 Jul 1764 to Thomas Hartley, she died 1780 - 7 children.
3) William - baptized at St Nicholas, Deptford on 22 Dec 1746, died before 1783.
4) Mary - baptized at St Nicholas, Deptford on 20 Nov 1748 was married at St Mary Magdelene, Woolwich on 27 Aug 1775 to Joseph Smith, she died before 1783 - 2 children.
Jean Touzeau (presumed to have been born in France) died in St Peter Port on 19 Oct 1719. He was twice married (1) Marie Guillebaud who was buried in Guernsey on 2 Sep 1704. (2) He married Marie Baudry on 13 Feb 1705/6 in St Helier, Jersey. He was the father of 22 children - (11 all male births were recorded in Guernsey parish records with Marie Baudry, which included a set of twins and a set of triplets, who did not survive). Marriage records for 3 sons of Jean's first marriage and 4 sons of his second marriage have been located.
Do hope this is of help to you.