Compile a Composite Image from Several Source Images

For a wedding save the date card, my fiancee would like to get a picture of our three dogs sitting in front of her homemade sign that says "Our humans are getting married." We have 22 images that are available on dropbox of our various failed attempts to get all the dogs in position and looking their best. The final image may be difficult to create because you'll want to eliminate the bland cement wall background, and you will have to isolate various elements (i.e. dogs and the sign) from several of the source photos and assemble them as seamlessly as possible. I have attached a few sample photos.