If you look at this page on the Pickwick site
http://pickwickfamily.org/p1.htm#i20you will see that Harriet Sainsbury married Charles Pickwick. It is this branch of the family which changed their name from Pickwick to Sainsbury.
Eleazer left his property to his wife and she had the choice of which property to reside in. After her death or if she decided to live in Queen Square in Bath his nephew William Eleazer Pickwick had the use of his other property. Eleazer was trying to keep his property intact so it was left to his cousin Moses Pickwick, or nephew William Eleazer Pickwick or nephew Charles Pickwick and their male heirs. If Moses had no male heirs then that property was for the use of his niece Martha Withy and her sons. If Martha had no sons then any daughters of Moses were to have use of the property. If Moses had no daughters then any daughters of Martha were to have use of the property.
Eleazer's sister Mrs Elizabeth Bullock was to receive an annual sum of £50 by quartely payments. After Elizabeth's death the trustees had to raise £2,000 which was to be paid to Martha Withy the daughter of Elizabeth Bullock.
In the codicil Martha is mentioned "my niece Martha Withey now Barrow". She and her children were to take the place of Moses Pickwick and his children. "my niece the said Martha Barrow late Withey now the wife of Charles Barrow Esquire an annuity of one hundred and fifty pounds by quarterly payments". Martha was also to receive £2,000.
You can download Eleazer's will for a small sum of money from
http://www.nationalarchives.gov.uk/documentsonline/Type Eleazer Pickwick in the search box and it should find the will.
I hope that this helps.
Copper