Elisabetta Grillo, 41, and Francesca Grillo, 35, who are accused of abusing their positions as housekeepers to splash out on luxury items, pleaded: "Somewhere in your hearts you will find a way to forgive us".
Prosecutors claim they lived the "high life", spending the money on designer clothes and handbags from Louis Vuitton, Christian Dior and Vivienne Westwood.
An email sent by the Italian sisters to Ms Lawson and Mr Saatchi was read out to the jury at Isleworth Crown Court, London, by prosecutor Jane Carpenter.
"We are at our utmost despair and we are reaching out to you in the sincere hope that somewhere in your hearts you will find a way to forgive us and believe that we never meant in any way to seem to be disloyal or to seem like we took advantage of our positions," the email read.
They told the couple they believed they had a "bond like a family", and saw them as mother and father figures.
"There is not a worst feeling thinking we have in any way let down our family and we are deeply sorry and full of regret," they wrote in the email in October, last year.
"All we want to do is put this right and make amends."
The sisters also forwarded the email to Anzelle Wasserman, the current personal assistant of Ms Lawson, who gave evidence yesterday.
The letter continued: "We asked our lawyers to try and settle this ongoing nightmare and we plead with you to find a way in your hearts so that we can stop the fighting, which is destroying us and make amends with you as soon as possible.
"This is all we wanted to do from the beginning of this whole nightmare.
"From the bottom of our hearts we extend an olive branch in the hope you will understand we never ever meant to hurt in any way.
"Please forgive us and help us put this right."
The sisters, of London, are accused of committing fraud by abusing their positions by using a company credit card for personal gain. They deny the charge.
The trial continues.