Their elder brother, Kelvin Cheng Ka-ki, 17, is also a member of the Hong Kong water polo team.
The 15-year-old twins recalled the days when they were studying at Hennessy Road Government Primary AM School and how one's misbehaviour can affect the other.
"I was once punished by a prefect for running on the playground and had to stand still during the whole recess. However, I slipped into the toilet when he was not looking. At the same time, Kenneth came out of the toilet and since we looked alike the prefect 'caught' him," says a smiling Kamil, who is two minutes older than Kenneth but three centimetres shorter.
Kelvin and his mum do not have a problem identifying the twins though. "They are totally different and I don't understand why people keep mixing them up. My mum also thinks so. But when I look at photos taken when they were children, they look the same to me," says Kelvin.
The twins' looks may change as they grow up, but they definitely share the same DNA. They started off as swimmers, but took up water polo inspired by their brother's success.
"We found swimming boring, and after watching Kelvin, we thought water polo would be more interesting. And we should thank our elder brother for teaching us the basics," says Kenneth.
The duo, who joined the Hong Kong team in 2009, play different positions. Kenneth is the goalie, while Kamil is a winger.
They are Form Four students at Tang Shiu Kin Victoria Government Secondary School, while Kelvin attends St Joseph's College. So Kelvin plays against his brothers in school tournaments.
The twins are in the same class this year because they picked the same HKDSE subjects. At the start, teachers were very confused and some still don't call our names during lessons, says Kamil.
They do the revision together and they have similar ideas. "When we write an essay or make a speech on the same topic, the content may be very similar. This can surprise the teacher," says Kenneth.
The twins know they cannot always be together, but separation can be hard sometimes. For example, Kelvin and Kenneth were named in the Hong Kong water polo squad for last year's Asian Games in Guangzhou, but Kamil missed out. "I was a little upset, but I was also very happy to see my brothers play for Hong Kong in such a great event," says Kamil. He and his parents were on the stands at the Guangzhou pool, cheering for the two boys.
But, come the 2014 Asian Games in South Korea, the twins are determined to be in the pool - along with Kelvin - battling to do Hong Kong proud.