First, let's see if they can be 2-digit house numbers.

Suppose the house numbers are XY and YX, where X and Y are digits.

Suppose XY is the larger of the two.

Then X is larger than Y.

So when we subtract larger minus smaller,

  XY
 -YX
   2 

we have to borrow from the X of XY, since X is bigger than Y.
so to get the 2 we are subtracting a digit X from a number 10 
or larger to get the 2. So we're either subtracting 10-8=2 or
11-9=2, for there are no digits larger than 9. It can't be 
10-8, for that would make Y=0, making the first digit of the 
smaller house number be 0.  So the only pussibility to get the 
2 is for us to be subtracting 11-9=2, which means Y=1 and X=9.
So the larger house number is 91 and the smaller one is 19. 

  91
 -19
  72 

Edwin