Re: how to combine pictures?
The first problem I see is the difference in resolution of the photos (since one is smaller than the others) first I would see what the final image size for printing is going to be and then make the canvas that size.
On the rest I would turn the photos to smart objects in order to size to my hearts content. Be informed that if the smaller photo is too small you'll get it pixelized no matter what you do when you upsize it. Also when free transforming remember to press the shift key before resizing so you maintain the original dimentions of the photo. Masking each layer is what I would do for a collage...
If you have a specific problem try to write about it since the only concrete problem you describe is the smaller photo, the rest of the process is a bit confusing, not sure what your real problem is there