Peter Farquhar, 69, and 83-year-old Anne Moore-Martin lived three houses apart in the village of Maids Moreton in Buckinghamshire and died within a year and a half of each other.
Church warden Ben Field, 28, and 32-year-old Martyn Smith, a magician, have been charged over the two deaths and are due to appear at High Wycombe Magistrates’ Court on Wednesday.
Both men have been charged with two counts of conspiracy to murder Ms Moore-Martin and Mr Farquhar, one count of attempted murder of Ms Moore-Martin and one count of murder of Mr Farquhar.
Field also faces two counts of fraud and three counts of burglary, while Smith is charged with one count of fraud and two counts of burglary.
It was understood that the two men cared for Mr Farquhar as his health deteriorated and were students at the University of Buckinghamshire, where he was a guest lecturer.
They are said to have encouraged him to publish his works, and set up a company to do so.
Mr Farquhar was a lay preacher at Stowe Parish Church where Field was listed as a deputy warden.
They were arrested in connection with the investigation on 16 January but were re-arrested on Tuesday.
A 22-year-old man from Olney was also arrested on suspicion of one count of conspiracy to defraud, one count of conspiring to commit fraud by false representation and one count of suspicion of fraud by false representation.
He has been released under investigation.