How do I detect if four smaller sprites are adjacent to one another to then turn into a larger one?

Hi there, I'm just experimenting with c3 a bit here & was wondering if anyone knew a simple way to achieve the detection of four sprites adjacent to each other ,or squares in this case, stacked in the form of a larger square & to then destroy those 4 sprites & replace it with the larger version in the same place that the original 4 were.

I've created an illustration bellow to better convey my meaning as I am finding hard to put into words.

Have a look at the modified version of your file. 1drv.ms/u/s!AkmrWgxeuxlKhIcr596sbSuJg3Rawg

I've set it up so that the small has instance boolean variables that indicate if it is overlapping to the right, below, and below&right. Then I've put the test for the overlaps into a function that is called when the sprite has arrived at its moveto location.

You only ever need to check for the offset at those three positions because if four squares are together that condition will always exist.

You can change when the function is called to suit whatever your game is about