Oh, I don’t feel the words like something you think
The resolution depends by the type of your game, so this design cannot written in engine.
But generally speaking, scale the background sprite to cover the fullscreen, and set 3 x 3 = 9 anchor points in the screen, these 9 anchors would be changed between different resolutions, e.g. by #ifdef #else #endif. Your sprites are relative to these 9 points using “x = anchor_x * scale + offset”.
AFAIK, many games maintain only one copy to support both iphone & ipad in this way.