Have a hud layer and have the two buttons, set it to invisible. Have the sprites with the scroll to behaviour and a booleon.
On double click sprite, set scroll to behaviour enabled, the booleon to true, and set hud layer visible.
This should zoom onto the chosen sprite, and the hud (set it to 0,0 for the paralax) should have the buttons open next to the sprite.
Then on click button, pick the sprite where the booleon is true, and either upgrade it's variables, or destroy it
Alternatively, you could spawn buttons at position sprite.x+40,sprite.y
And spawn the other at sprite.x-40,sprite.y
You would still need a booleon. The first option just saves you from destroying buttons.