The men took the family of Laurence Kennedy hostage at the house in Holywood, Co Down, in November 1991, then lay in wait for him to return from a medical conference in England, Belfast Crown Court was told.
But Dr Kennedy's wife Sarah alerted police, using a secret alarm, and this led to an armed siege. The men eventually surrendered after negotiations conducted through a priest.
Francis Maher, 27, John Glennon, 28, John Kennaway, 31, and Damien Morgan, 24, all of Belfast, were sentenced to a total of 100 years' imprisonment after being found guilty of the murder conspiracy.
Mr Justice Pringle rejected the men's claims that they had intended only to commit a robbery at the home of Dr Kennedy, 45, a founding member of the Conservative Party in Northern Ireland.
The judge said: 'You must have intended to murder him for his political views although these were non-violent.' As the sentences were passed, the men struggled with warders in the dock as screaming relatives, shouting republican slogans and cursing, wrestled with police in the public gallery.
The judge praised Mrs Kennedy for her 'coolness and courage', which led to the foiling of the murder plot.
The four men were also given concurrent sentences - ranging from 10 to 20 years - for possessing a loaded handgun and for holding the Kennedy family hostage.Reuse content