I really try and take a relaxed approach to family pictures. I get the group and posed shots out of the way first because kids tend to lose interest fast. Then, I just let the kids do whatever they would like and I take pictures as they have fun. I will direct them a bit but really what I want to capture is them being happy. Even my kids look strange when I ask them to smile for the camera. Parents will often try and be helpful by telling the kids to smile while standing behind me, although I appreciate the help, in this case it's best to let me do all the asking as kids will often get confused on where to look as well as feel pressured to take pictures and that usually ends up with them wanting nothing to do with the camera. Just relax, some of my favorite shots are those with no requested smiles.
This is probably the most asked question when dealing with family photos. My suggestions are to choose classic item. Things like jeans or khaki, paired with white or another neutral are a few of my favorites. Don't be too matchy (yes I am aware that is not actually a word but hey, neither is "pinteresty" but I use that too). Although some themed shoots are designed to have matching outfits, and look great, I generally advise having everyone dress similar but not identical. Adding splashes of color for each family member can be visually appealing as well, a red flower in the hair, belt, bracelet etc can be a great way to tie all the outfits together without being overkill. I always tell mom, go find something you feel pretty in and them build the family's outfits around that. Sometimes all it takes is that first outfit to get you inspired for the rest of the family.