By a chance I got in touch with your message in this Forum. I have the exact answer. Elizabeth Brock (1767-1847), only surviving sister of Sir Isaac was my ggggrandmother. She married the shipowner and merchant John Elisha Tupper Esq. of Les Cotils and Carrefour in Guernsey.
Ferdinand Brock Tupper (1795-1874) the great historian of the Channel Islands, author of "The life and correspondence of Sir Isaac Brock K.B."(1845), states in this important book that the general's parents John Brock Esq. and Elizabeth de Lisle, had in fact 14 children (4 women and 10 men). But, the different genealogical trees from the Brock family available in The Priaulx Library, Candie Garden, Guernsey, only mention 13 children. Only 10 of them became adults. According to that information, the children in strict order of birth were as follows:
1. Rebecca, born in March 4th 1758, died as a girl;
2. John, born April 13th 1759. Lt Col in 81st Reg. Killed in duel July 1802, in Cape of Good Hope. Died single, no descendants;
3. Ferdinand, born June 15th 1760. Lt in 60th Reg. Killed at Baton Rouge, first American War, Sept 21th 1779. Died single without descendants;
4. Peter Henry, born July 1761, died as a boy before 1765;
5. Daniel de Lisle, born December 10th 1762. Bailiff of Guernsey 1821-1842, one of the greatest political leaders of the Channel Islands. Died September 24th 1842. Married 1798 with Esther Tourtel; two children, Eugene and Sophie;
6. William, born June 23rd 1764. Head of the Bank of W. Brock & Brothers, in the City of London. Died in London. Married Sarah Maria Pitt (called Sally), cousin of Lord Rivers and a relative of Lord Chatham. No descendants, but they raised their three orphan nephews Potenger;
7. Peter, born in August 6th 1765, died in childhood;
8. Elizabeth, born January 2nd 1767, died October 30th 1847. Married in 1789 with John Elisha Tupper Esq, twelve children: John Elisha, Henriette, Mary, Ferdinand Brock, Ernest William, Charles James, William De Vic, Brock, Frederick, Octavius, Carey and Caroline;
9. Frederick, born in October 3rd 1768. Died single, no descendants, in Montpellier, France, 1803;
10.SIR ISAAC, born October 6th 1769, killed at Queenston Heights in October 13th 1812;
11. Mary, born April 25th 1771, died in 1798. Married with Thomas Potenger Esq., three children, William, Mary and Zelia;
12. John Savery, born October 22th 1772. Aid-de-camp of both Sir Ralph Abercromby in Hollandand Sir John Moore in the Peninsular War. Died August 7th 1844. Married twice: 1º Elizabeth de Jersey, four children: Julius, Elizabeth, Rosa and Betsey.
2º Elizabeth de Lisle;
13. Irving, born May 23th 1775. Associated with is brother William and J.E. Tupper at the London bank; writer and translater of "Bernier's travels in India", and a friend of Prime Minister Spencer Perceval. Died in 1838 in his home at Bath. No descendants.
When Sir Isaac died in 1812 there were only one sister and four brothers alive: the said Elizabeth, Daniel de Lisle, William, John Savery and Irving. There were 17 direct nephews of the celebrated general, four of them were Brocks (only one man, Eugene), ten were Tuppers and three were Potengers. When captain Eugene Brock, only son of Daniel de Lisle, died in 1844, in Bermudas, extinguished the closer male descent to Sir Isaac. The number of alive nephews and with descendants was substantially reduced. With the time it was also reduced the number of beneficiaries with the lands that the British Crown gave to the inheritors of Sir Isaac, lands that part of them were in Waterdown, near Hamilton, Canada, and its settlement was organized by Ferdinand B. Tupper.
Actually, the great majority on the closer relatives from the Canadian hero are named Tupper, and live in Great Britain, Chile, New Zeeland, Brazil, Venezuela, Costa Rica and the United States. In the States the descendants belong to the branch founded by the engineer Eugene Tupper in Portland, Oregon, who born in Santiago de Chile in 1941, and married twice with three sons.
It is interesting to add that the actual Chilean ambassador in the United States, Mr. Andres Bianchi, belongs also to the Chilean branch of the Tuppers from Guernsey and also carries the glorious blood of Sir Isaac Brock.