His mother had lived a "challenging life" but he felt she had recently been moving towards "the light at the end of the tunnel".
Her daughter Rachel, 19, also felt sympathy for Muller who "has to live with this for the rest of his life".
Muller, a master cabinet maker, earlier pleaded guilty to a charge of careless driving causing death.
The court heard that Muller "unreservedly apologises" for the accident which had such tragic consequences for the Ellis family.
He was in New Zealand for a three-month tour of the country and had purchased a motor vehicle in Auckland.
The night before the accident, he camped south-west of Christchurch with a group of fellow German travellers he had met.
At 10am, they set off, with Muller driving with one passenger, and the other vehicle with five people travelling behind.
He told his defence counsel that he never saw the stop sign.
"He simply missed it," the court heard.
The windscreen was "a little bit foggy", the court heard, possibly because of damp or dewy tent and camping equipment in the vehicle.
Judge Raoul Neave said the impact of the tragedy on the Ellis family was impossible to measure.
He noted that Muller was genuinely remorseful, devastated by the accident, and had cooperated fully with a restorative justice conference - something that the Ellis family have found benefit from.
Judge Neave ordered Muller to pay emotional harm reparation of $7500 to both of Ms Ellis' children - $15,000 in total - by Thursday. Muller must also pay $450 for damage to a fence, and is disqualified from driving for nine months.
