Lockerbie bombing archive
Libyan Abdelbaset al-Megrahi was jailed for life for the bombing. He died from cancer last year.
Dr Jim Swire lost his daughter Flora when Pan-Am flight 103 exploded, but he does not believe Megrahi was responsible.
He told the BBC: "We have the right to know everything the government knows about who it was that killed our families.
Megrahi died at his home in Tripoli in May last year from terminal cancer. He had always protested his innocence.
His brother Abdel-Hakim Al-Megrahi said the family "wanted the truth to be revealed".
He also said he was hopeful the Libyan government would help to fund the appeal.
In an interview with the BBC's Libya correspondent Rana Jawad, he said: "Yes, we want to appeal and we wish for the truth to be revealed and this is not just for our own benefit but also for the benefit of the families of the victims and for public opinion.
"We need to know who committed this horrible crime. But, as you know, we as a family cannot afford to pay for the appeals process.
Abdel-Hakim Al-Megrahi insisted his brother had not been a Libyan intelligence officer, and claimed he had instead been a graduate in aviation engineering who had been employed by Libyan Airlines.
Abdel-Hakim Al-Megrahi insists his brother was innocent
Megrahi was found guilty at a trial in 2001, and jailed for life. His co-accused Al-amin Khalifa Fimah was acquitted....
Dr Jim Swire, whose daughter Flora died when the Pan-Am flight 103 exploded over Lockerbie in 1988, said earlier this week that some families of those who died may seek a fresh appeal against Megrahi's conviction.
Mr Swire believes that Megrahi was wrongfully convicted of the atrocity.
But Scottish and US investigators stand by the evidence presented at his trial and are pursuing other potential suspects.
In a BBC interview on Monday, the Lord Advocate Frank Mulholland said "the conviction stands".
A spokesman for the Crown Office said:
The 25th anniversary of the bombing, which claimed 270 lives, will be marked in ceremonies in the US and the UK on Saturday.
Families consider Megrahi appeal
A fresh appeal against the conviction of Abdelbaset al-Megrahi for the Lockerbie bombing may be sought by UK relatives of some of those killed.