+1 what Tony said. Let me add just a couple more tips. Use a tripod. There are a couple reasons. This will allow you to set up the camera and you can move, even if only your head. I prefer with a shot like this to bring my head up just above the camera and make eye contact with the folks without looking through the camera for the shooting. Their heads slightly tipped up to look at me vs dead on to the camera often is more appealing.The other thing with a tripod is take numerous shots of each pose in rapid succession. One thing with groups is everyone looking where you want them to, and all eyes open at the same time can be more of a challenge than you think, particularly outdoors. With multiple rapid captures you can always PP and align 2 shots and paint in a subject or 2 if needed. The other thing I would suggest is to bracket your shots. Just to be sure you get the exposure you're looking for. Hey, you could even play with some HDR effects after the fact. Good luck.

Oh one more thing on the poses. Try some different poses. Tony's tips are spot on but I would add some others with maybe them sitting in the grass etc. Just google family portraits and look at some samples or go down to the local barnes and noble and pick up a book on poses, they have some pretty good ones. The one thing I will repeat that Tony already stated is, keep them close.