Martyn Smith and Benjamin Field are also accused of fraud and of stealing a number of rifles.
Thames Valley Police launched a double murder inquiry in January, more than two years after the death of Peter Farquhar (pictured above), 69, a guest lecturer at the University of Buckingham, and seven months after the death of retired headmistress Ann Moore-Martin, 83.
Mr Farquhar died on 26th October 2015, and Ms Moore-Martin, who lived three doors down from him in the village of Maids Moreton, near Buckingham, died on May 12, 2017.
Field, 28, a church warden, and 32-year-old Smith, a magician, appeared at High Wycombe Magistrates' Court on Wednesday.
Field, of Wellingborough Road, Olney, is charged with two counts of conspiracy to murder Ms Moore-Martin and Mr Farquhar, one count of murder of Mr Farquhar, one count of attempted murder of Ms Moore-Martin, two counts of fraud and three counts of burglary.
Smith, of Penhalvean, Redruth, Cornwall, is charged with two counts of conspiracy to murder Ms Moore-Martin and Mr Farquhar, one count of murder of Mr Farquhar, one count of attempted murder of Ms Moore-Martin, one count of fraud, and two counts of burglary.
Both men are accused of stealing a French carbine rifle, an African long gun and a Martini-Henry rifle in April 2016, the court heard.
They are alleged to have committed fraud in 2016 by falsely claiming another man, Thomas Field, had kidney problems and needed a dialysis machine worth more than £26,000.
And Ben Field, who appeared in court with a cropped beard and a white fleece top, faces a charge of stealing a cardigan and a bottle of Drambuie.
Smith and Field were remanded in custody and are due to face Oxford Crown Court on Thursday morning.
A 22-year-old Olney man, who was also arrested on suspicion of conspiring to commit fraud by false representation and other charges, and has been released under investigation.
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