Richard Davies, 41, died of a single gunshot wound to the chest after firing at officers in St Neots, Cambridgeshire, in October 2015.
His widow Samantha said she had a text from her child saying they were tied up and begging her to "call the police".
Mr Davies was shot after firing a gun from the house. The inquest continues.
The father of three said he "wanted to end his life" after learning his marriage was over, the hearing in Peterborough was told earlier this week.
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Giving evidence at the hearing, Mrs Davies said she had initially believed her husband had "some acceptance" about the end of their relationship and said "there wasn't an ounce of anger" during their conversation earlier that day.
However, he had made several trips to a nearby shop to buy alcohol and had been carrying a knife, the inquest heard.
Mrs Davies went to visit her sister and when her children returned to the family home their father tied them up.
The inquest then heard how the children managed to make 999 calls and alert their mother.
She received a text that read: "Call the police. Get them to come to our house. Dad's going to kill himself. He's tied us up. I'm not joking."
When Mrs Davies arrived, one child had managed to escape.
She said when Mr Davies came to the door "he didn't really look like my husband".
He returned a short time later with a knife pointed at his chest, she told the hearing.
Her other children managed to escape and Mrs Davies was taken to a neighbour's house.
Mr Davies was shot dead by a police marksman after firing six shots from the house, the inquest heard.
Mrs Davies said she had never seen his home-made gun or ammunition before, and her family was "forever changed" by what happened.
The inquest continues.
The widow of a man shot dead by police has told an inquest of a desperate text sent by one of their children saying "dad's going to kill himself".