Paddy said since coach Johnson had come on board at Swim Rotorua a few years ago he had made huge leaps with his swimming.
"I had never made B nationals before he came and now I'm in the New Zealand team," he said.
Paddy has been selected to race in his favoured freestyle discipline, while Jack's specialty is breaststroke.
Paddy explained he was more of an endurance swimmer, doing best in longer distances, while his older brother was more of a sprinter.
Like most brothers, the pair enjoy racing against each other and have their closest races during training across the middle distances.
"So over the middle ones like the 200 and 400 it is very close," Jack, 17, said.
Jack said while they do long hours in the pool for training, making small gains and breaking personal bests always added new motivation to keep going.
He said Johnson was really helping them get gains in the pool and he was rapt to make a New Zealand squad for the first time.
Johnson said the two swimmers were preparing well for their trip to Aussie.
"We know that the competition will be fierce against the Australians. However, they are training well and we are confident that they will race even faster in four weeks' time."
Paddy and Jack both have the same parents but Paddy has kept his mother's maiden name. The pair both attend Rotorua Lakes High School.