Lauro Bertulano, 46, and Rebecca Jones, 31, neglected patients on a specialist stroke ward at Princess of Wales Hospital in Bridgend.
A third, Natalie Jones, 42, was given a community order for the same offence.
Cardiff Crown Court heard they failed to check blood glucose levels at least every two hours on multiple occasions.
All three previously pleaded guilty to multiple charges of wilful neglect.
Rebecca Jones was sentenced to eight months, Bertulano to four and Natalie Jones was given a 12-month community order.
Sentencing, Judge Tom Crowther QC said: "I pause to remind myself that you all would have seen worried relatives coming and going, sitting with their mothers, fathers or spouses as they lay ill, some approaching the end of their lives, and to wonder with bemusement how you could have continued to betray your patients and those families as you did.
"This was not a failure to do your job, it was a failure of compassion and humanity.
"This was clear-eyed and calculated deception, the purpose of which was to make the defendants' working time easier.
"There was also... a real risk to health, even if that risk happily did not materialise."
In a statement read to the court, Gareth Williams, whose mother Lilian's records were falsified by all three defendants, said the family had been left "completely haunted and traumatised" by their mother's treatment after their repeated complaints to staff were ignored.
"During those tortuous months each dreadful day was an eternity that seemed to merge into a long nightmare," he said.
His sister, Christine Williams, said the experience had completely destroyed her faith in the medical profession, adding: "I no longer believe we have a health service to be proud of."
Abertawe Bro Morgannwg University Health Board offered "sincere apologies" to the families involved and said it would be contacting them with an offer to meet and answer questions.
It said in a statement an internal review had established no patients had been harmed by the nurses' actions, but apologised again for "the distress caused.
"We are also now able to commission further work to consider what can be learned from these events, and to ensure we have everything in place to avoid it happening again," the statement read, adding internal proceedings were under way with 12 other nurses suspended from work.
Chief executive Paul Roberts said he was confident that the practices uncovered in the investigation were "not widespread".
Rebecca Jones had admitted nine charges relating to nine patients, Bertulano to six charges and Natalie Jones to two, all relating to the period between 2012 and 2013.
The court heard concerns were first raised in February 2013 when there were discrepancies between blood glucose levels recorded in patients' notes and readings on a glucose meter taken by Rebecca Jones.
She was suspended and an investigation of the ward was launched.
It found that in total, she made 51 fake entries in patients' notes, Bertulano made 26, while Natalie Jones made four.
Patients on the ward should have been routinely tested every two hours, but one went 26 hours without being checked.
The court heard the absence of such tests could be potentially harmful to those unable to regulate their own blood glucose levels.
Nicholas Gareth Jones, defending Rebecca Jones, said she was unhappy at work and felt stressed but had no explanation for her actions.
Matthew Roberts, defending Bertulano, said he was under "considerable" pressure at work and all his false recordings were made on night shifts when there were only two workers on duty.
Kevin Seal, defending Natalie Jones, said she accepted she had cut corners in a bid to complete her work but had believed she could play "catch up" later.
Two nurses who failed to carry out blood glucose tests on patients and then faked the results have been jailed.