The move by Kent shop manager Martin Rose, which includes suing for his own crash injuries, prompted condemnation from the guardians of orphaned Emma Lucas and anti-drink drive road safety groups.
Mr Rose, who served 10 days of a five-month sentence following the accident, was branded "callous beyond belief" and "cold-blooded" yesterday by the Campaign Against Drink Driving. He was also criticised by his local MP.
The accident near Ashford, Kent, in May last year saw Mr Rose's van collide with a Mini carrying 34-year-old Trudy Lucas, her husband Peter, 65, and their children James, 10, and Emma, then aged seven.
The parents were killed instantly and James died two hours later at the town's William Harvey Hospital. Emma was not expected to survive but battled back from appalling injuries.
Mr Rose, who has two previous convictions for drink driving and another for failing to provide a specimen, was convicted last year of failing to provide a sample of blood for analysis after the accident. He served 10 days of a five-month sentence before his release pending an appeal.
Mr Rose's solicitor's letter, sent this week to Trish Dodsworth, Mrs Lucas's mother, alleges Mrs Lucas was responsible for the accident.
Ashford MP Damian Green said: "It's appalling that he is seeking to prolong the family's agony in this way."
Maria Cape, of the Campaign Against Drink Driving, said: "This man must have a heart of stone to act in such a cold-blooded way against this family."Reuse content