Nyachwo is said to have found the Opongs having a lunch of cassava bread and offered them smoked fish.
Police in Tororo district are holding a woman suspected to have poisoned four people from the same family reportedly over the Standard Gauge Railway compensation money.
Joyce Nyachwo was arrested from her home on Friday after the head of the murdered family members, Okum Opong, reported the case to local police.
Tororo district police commander, Robert Katuramo said Nyachwo is a resident of Ayira zone in Nagongera sub-county, the same area the deadly incident happened.
It is said the family was poisoned through food.
It is not exactly clear what circumstances led to the act but unnamed sources told New Vision that the family had bought a piece of land near the Standard Gauge Railway at sh6m. Then came the time of compensation.
Details are shallow but according to the sources, the sellers of the land must have gotten jealous that the family would be getting sh16m as compensation. And so the original sellers hired Nyachwo to kill the family members, according the sources.
Two of them died the day they were supposed to be compensated.
Earlier that day, Nyachwo is said to have found the Opongs having a lunch of cassava bread and offered them smoked fish. It is understood she did not taste the fish - she only ate the vegetables.
But something was not right.
Shortly after the meal, the members complained of stomach aches, with form coming out of the mouth of some.
Margaret Abbo died in the morning while Rose Awori passed away on the way to Tororo Hospital. The other two - Gloria Acheng and Rose Awor - are still receiving treatment.
Residents, according to Police's Katuramo, heard screams from the house. They took them all to Nagongera health centre but that their situation worsened, prompting medical personnel there to refer them to Tororo Hospital.
When New Vision visited health facility, nurse Annet Nabwire said the patients were improving steadily.
The suspect is said to be a longtime friend to the family.
Nabwire said the victims were food poisoned but that postmortem examinations will be carried out to establish the exact cause of death.
Local police say more cases of food poisoning have been reported in Tororo, including one where two families were poisoned through food in the last one month.
Three students of Mukuju Core Primary teachers College died after being poisoned. The suspect is still in custody and is set to appear in court to answer charges of murder.