The twins were born at 32 weeks by emergency caesarean during a sometimes harrowing labour where they appeared to be struggling to breathe.
"They managed to find a heart beat, but the breathing was very shallow," Mr Howie told the Nine Network's A Current Affair.
He said he was initially shell shocked when he saw his babies, but was also felt prepared.
"I am proud as punch to see them make it this far, where all the odds were against us," he said.
Their mum thinks they are "amazing".
"I think they're beautiful, Simon thinks they're beautiful, really that's all that matters," Ms Young said.
Doctors have told the parents that they do not know what the future holds for the babies and they were still in "unknown territory".
"As long as they're fighters and they keep fighting they will be ok," Mr Howie said.
Doctors discovered the babies' condition during a routine ultrasound at 19 weeks and their parents went against medical advice when they continued with the pregnancy.
- AAP