John and Marjorie Ann Scarle were found dead from hypothermia at their bungalow in Eastwood Road North, Leigh-on-Sea, Essex, in 2016 - triggering a dispute over their joint assets.
In a case described by lawyers as "extraordinary", Mr Scarle's daughter Anna Winter and Mrs Scarle's daughter Deborah Cutler went to the High Court over their inheritance.
Ms Winter's case was that forensic evidence suggested Mrs Scarle, 69, died first, resulting in her father inheriting all of the couple's assets before his death - which would then pass to her.
But Ms Cutler relied on a 100-year-old law which creates a "presumption" that, as the elder of the two, Mr Scarle, 79, died first - meaning she would inherit the assets through her mother.
Ruling in favour of Ms Cutler, who now stands to receive all of the £300,000 estate, Judge Philip Kramer said he could not be certain which of the pair died first.
The judge said the couple, who were both in poor health, were found dead by police on October 11 2016.
Ms Cutler said she last spoke to her mother on October 3 and sent the couple a card for their wedding anniversary, which had been opened.
She also tried to call them on October 7, but received no answer and assumed they were out celebrating their anniversary at a Chinese restaurant, as they did each year.
Delivering his ruling on Tuesday, Judge Kramer said forensic evidence suggested Mrs Scarle died first, because her body was more decomposed than that of her husband.
But he said he could not rule out that the different rates of decomposition could be explained by the difference in "micro-climate" between the toilet, where Mrs Scarle's body was found, and the lounge, where her husband was discovered.
He said the presumption in favour of the older person dying first, enshrined in the Law of Property Act 1925, would therefore apply.
The court heard Ms Cutler had offered to settle the case by dividing the assets, including the couple's home, equally between herself and Ms Winter.
At one stage she also offered a 60/40 split in Ms Winter's favour, and to enter mediation in an attempt to resolve the dispute.
However, all offers were rejected and Ms Winter indicated she would only settle the case out of court if she could have all of the assets.
James Weale, representing Ms Cutler, told the judge: "This claim should never have got to trial - it was always a case which cried out for settlement.
"For her part, short of capitulating, (Ms Cutler) could not have done any more to resolve this dispute.
"However, she was met with stubborn intransigence on the part of (Ms Winter) who refused to make any reasonable attempt to engage in settlement negotiations at any stage."
Judge Kramer ordered Ms Winter to pay the majority of Ms Cutler's legal costs of £84,000.
She also faces a bill of about £95,000 for her own legal costs.
The judge said a number of "unpleasant responses" online to earlier reports of the case had been drawn to his attention.
He said there was "no suggestion" either Ms Winter or Ms Cutler, who had been upset by the comments, were "otherwise than attentive towards their respective parents".
He added: "Those who have been speculating about what was going on in the family just really have no basis for it at all.
"It is just so sad that people can be so vitriolic about something about which they know nothing."
Speaking after the ruling, Ms Cutler's solicitor Rachel Liebeschuetz, of law firm Law Hurst & Taylor, said: "The judgment provides welcome clarification to this area of law, which has been uncertain for many years."