The trio will be Ireland's only sailing representatives and will compete in the three-person keelboat event in the Sonar.
Twomey is a Paralympics veteran and will be making his tenth Games appearance at London 2012. Speaking to the Irish Sailing Association at Sail for Gold, Twomey said, "In my former life I was a discus thrower up to 1996 and took up sailing for the Sydney 2000 Paralympics.
"We are very much on schedule for what we want to achieve training and competition wise. We've a lot of work to do but the boys are bringing it in and we are well up for it."
For Hegarty and Costelloe it will be their first Paralympic Games and Costelloe is thoroughly enjoying it, "I find it great. My two crew are very good to me and look after me well but we've got a lot of work to do between now and the Games," said Costelloe. "I'm sure if we do a lot of work between now and then we'll move up the fleet and hopefully into the top three."
The Paralympic Sailing Competition will run from 1-6 September 2012 at the Weymouth and Portland National Sailing Academy.