Paul Welbank reports that George and Margaret had seven children:
Elizabeth, b. 3 Feb 1733/4
Jane, b. 26 Sep 1735
Margaret, b. 27 Jun 1737
Christopher, b. 16 Jul 1739, Gainford, Durham d. bef 1790, m. Ann Knapp on 1 Nov 1779 at St Andrew, Holborn. (Paul’s ancestors)
Robert, bapt 16 Jul 1739, St Mary's Gainford, Co Durham and bur. 4 Nov 1740 also at St Mary's Gainford.
William, my 3xGt-gf.
Mary, b. 3 Feb 1742/3, Stockton on Tees, Co Durham.
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This was found at <http://www.british-history.ac.uk/report.aspx?compid=76350>; in a list of gravestones in Stockton, Co Durham, churchyard:

“Margaret, daughter of George Welbank, and wife of George Brown, Gent. ob. Nov. 14, 1776, in the 40th year of her age.”

I wonder if this is the above daughter born in 1737?  The age is right.  If so, this gives her husband.
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A search on FindMyPast’s will and probate indices gives these two entries:

First name(s)       George
Last name           Welbank
Year                1768
Date                1768, FEB
Place               Greenwich
County              Kent
Country             England
Court               York Prerogative & Exchequer Courts
Court detail        Prerogative Court of York
Document type       Will
Document reference  vol.112, f.41
Index reference     1757061770120446.tif/25
Document ordering   http://www.york.ac.uk/borthwick/remote-services/copying/order-form/
Record set          Prerogative & Exchequer Courts Of York Probate Index, 1688-1858

First name(s)       George
Last name           Welbank
Year                1768
Date                1768, FEB
Place               York
County              Yorkshire
Country             England
Court               York Prerogative & Exchequer Courts
Court detail        Prerogative Court of York
Document type       Will
Document reference  vol.112, f.
Index reference     1757061770120446.tif/26
Document ordering   http://www.york.ac.uk/borthwick/remote-services/copying/order-form/
Record set          Prerogative & Exchequer Courts Of York Probate Index, 1688-1858

This looks like two entries for the one will, one for Greenwich, one for York.

I have filled in their order form at the above address and hope I will get somewhere useful with it.

I placed the order with payment in November 2020.  I received the copy in Mid-March 2021 and it was almost illegible.
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His will was signed on the February 1762.  It also had the date of 26th February 1768 at the end.  He described himself to be late of Greenwich in Kent and now of the the City of York; he had properties at North Cowton Ravensworth and Wharton in the north Riding of Yorks and at Poinsbridge in County Durham.

He appointed his wife Margaret and his son William as joint executors.

In the will he also mentioned his four daughters, Margaret who was married to George Brown, and Elizabeth, Jane and Mary.
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