I don't recall ever seeing a tutorial for making a double exposure in CA2 but one way to achieve 'that look' could be:
Start with 3 layers - Background layer plus No.1 and No.2 above
Add your 'top' photo (probably a cutout?) to Layer 1 and then Copy & Paste that photo to Layer 2.
Add your second photo to the Background layer
Click the 'M' symbol on Layer 1 to make that a 'Mask' Layer
Increase the 'Transparency' of the photo (the Transparency slider in the Colour Tab) on Layer 2 (the copy of the top photo at the top of the pile!) to let the photo on the bottom layer show through. You can then move the bottom photo around to get the positioning just right.
I hope this might help.......perhaps someone else will come along with a better solution!
I use a few layers building it up gradually.... Background with photo ..then another photo on a layer above...transparency is done in small pieces and saving as picture as you go.... If the transparency is done a little at a time like this ..it is more controllable how you would like the finish to be..