What is the difference between swing corner – oblique (RC82122) and swing corner – right (RC82222)?

Both will help create a sturdy robust swing frame. The oblique corners mean that the legs will also splay out to the left and right where as the right corners mean that the legs will come down from the top beam at 90 degrees. If you are building a double swing frame only use the oblique corners, if you want to build a swing frame with a slide alongside use 3 x right corners.