The court heard the 57-year-old woman's husband and younger children were home in bed at the time.
The Crown says the bullet was meant for Fisi'ihoi's eldest son after a botched gun deal.
Falala Iongi, Valiami Iongi and Manu Iongi appeared on Tuesday for the first day of their trial together in the High Court at Auckland in front of Judge Grant Powell.
The trio all pleaded not guilty to the murder of Meliame Fisi'ihoi.
Brothers Falala and Valiami Iongi also pleaded not guilty to charges of discharging a firearm with intent to cause grievous bodily harm and wounding with intent to cause grievous bodily harm at an incident that happened in late 2019.
Both shootings took place at the same location and were intended for the same man, Stephen Fisi'ihoi, the Crown says.
Instead Fisi'ihoi's mother was found slumped over the back of the couch facing out the window, which had a bullet hole in it.
"Her right arm was still holding the curtain ajar," Crown prosecutor Sacha Norrie told the jury on Tuesday afternoon.
"The accused were willing to let the gun do the talking."
A second Crown prosecutor told the jury how Fisi'ihoi and Falala Iongi's friendship dated back 10 years.
The Iongi brothers, their cousin Manu Iongi, and Fisi'ihoi were all members of a faction of the Crips gang.
Fisi'ihoi appeared via an audiovisual link this afternoon to give evidence.
The 34-year-old told the court how Falala Iongi asked for him to source a shotgun in return for some drugs.
"I traded the meth in return for the shotgun," Fisi'ihoi said.
He told the court how Falala Iongi was not happy with the gun and demanded to have the methamphetamine returned, but he Fisi'ihoi longer had the drug.
"He then got angry because it wasn't good enough so I told him to go do it himself," he said.
"What started as a firearms deal gone wrong escalated to a shooting and then ultimately a murder," Norrie said.
In opening submissions, Manu Iongi's lawyer, Simon Lance, told the jury to treat the accused as three separate offenders.
"Evidence could relate to one of the offenders. It would be wrong to relate all evidence to all three men.
"Sure Manu is an Iongi but he is an individual.
"It's not as easy as saying well if you were at the place of the offending then you are guilty," Lance said.
The trial is set to continue for the next five weeks.