I did it about the same as Bob. I used Photoshop all the way. When using Photoshop you can go about doing the same things but in different ways. Our way is usually the most common way for us not always the quickest way.
1) I opened both pictures into photoshop separately.
2) Big guy (BG) used the magic wand and selected him. Copied him and went to group picture and pasted.
3) Had to decide how big he should be. I looked at the knees and thought most everyone has about the same size knees and made BG the proper size with command T using transform and made him larger clicking a corner while holding shift key and pulling out.
4) Now that I had him about the right size I changed my BG layer opacity to about 45. I could now see both pictures and tried moving BG around to see how he best fit in and as you can see we both thought on the right. Returned opacity to 100%
5) Now having decided that I used the magic wand tool and selected most of the area that he would be in on the group picture and made a mask.
6) Make sure your group picture is unlocked. Move BG layer to bottom of layers. Now with the move tool move BG till you have him in place where you think appropriate. I had a hard time deciding if I should turn him a little counter clockwise but decided against it because his legs looked off.
7) Now cleaned up mask on group picture around BG. Done.

I am sure this is basic stuff for many Hogs but hope it helped some beginners with layers and masks. I learned the most from lessons on CreativeLive.com
Jim