Teenager Osrin will represent Great Britain at both the World Junior Championships in Budapest and the European Junior Championship in Kazan.
Dunn, meanwhile, has been selected for Britain’s World Para-Swimming Championship squad.
A recent newcomer to para-swimming, Dunn earned his spot on the team for London after a fantastic performance at the British Para Championships in Glasgow, where he broke the world record for the S14 100m freestyle and set a new British record in the 100m butterfly.
Dunn, who works for his dad’s carpet fitting business, said: “It’s very exciting to finally get to represent PL and GB on the international stage.
“I’ve been at the club since 2006 so it’s nice to finally have a breakthrough in the sport. After so many hard times it makes moments like this feel all the hard work has paid off.
“I’d like to thank my family for all their support over the years as without their help I wouldn’t be where I am today. Also all the hard work that (Leander head coach) Robin (Armayan) has done with me and everyone over the past two years and for the future.”
Osrin is also relishing the chance to represent Great Britain at the World Junior Championships and then the Europeans.
“I am really excited,” said the Plymouth College pupil. “It has been quite a big goal of mine. I have been working towards it so I am really happy.
“I am just going to be training hard now for the World and European Juniors.”
Osrin grew up in South African before moving with her family to Plymouth in 2016.
She was eligible to swim for both nations but opted for England and Great Britain. She was part of the England team that went to the Nice International earlier this year and returned with a medal.
“That went really well,” said Osrin. “I am proud to be representing England and GB. It kind of just came naturally. I had to decide and that is who I picked.”
Moving countries at a young age might have brought some culture shocks, but Osrin has really settled in Plymouth.
“I really like everything here,” she said. “I have settled in nicely.
“But the swimming is the best thing. It is so professional and the facilities are amazing.”
Osrin will be joined at the European Junior Championships by her Leander team-mate Sophie Freeman.