Jack and Paul Sykes, aged 12 and nine, died when their father Darren, 44, set fire to the property in Penistone on 22 October 2014. Mr Sykes was also killed.
During the service at St John's Church in Penistone, Claire Throssell recited words from the last Mother's Day card she received from Paul.
Candles will also be lit at 17:00 GMT and two doves released after the vigil.
Ms Throssell said: "It's an extremely painful day today. A few weeks ago, from one of my bag's, Paul's last Mother's Day card fell out.
"I read it again and I was stroking it because I knew his hands had touched it and the words in it were so beautiful.
"I thought these words need to be heard... so I just thought it was a good time to do that today, on Mother's Day.
"It's a very poignant day, which is why I wanted to do something positive to keep the boys' memories alive and keep that love burning for them, rather then being dimmed by despair and hate really."
Ms Throssell is also a supporter of the Women's Aid charity and is backing its campaign to protect children from abuse and domestic violence.
An inquest into the boys' deaths heard they had been lured to their father's home with a new model train set before Sykes, who had recently separated from Ms Throssell, set fire to the building.
Sykes and Paul died in the fire, while Jack died in hospital six days later.
A coroner ruled both boys had been unlawfully killed and recorded a verdict of suicide in the case of their father.
The mum of two boys killed in a house fire started deliberately by their dad has held a vigil to remember her sons.