I agree about switching foods; diet is, after all, the cornerstone of good health, so why not feed the best you can?

With the puppies, be wary about them getting too heavy - it is far more desirable for them to be lean than even slightly overweight. (In fact, I was just reading some research showing that dogs who were overweight when young were more prone to tumors later in life.) You should be able to see the outline of the last 2-3 ribs, and when you feel their ribcage it should feel like the back of your hand. So long as their hips and spine are not especially prominent, and they're eating/playing/eliminating/drinking normally, they are at a good weight. Boxer puppies will go through "walking skeleton" phases when you can see every rib from across the room - these generally last about a week, and then they go through a phase where it looks like their skin is just hanging off of them.
I personally don't recommend free-feeding, especially with multiple dogs. Along with it making housetraining much more difficult, since the dogs aren't on any schedule, controlling the food is one of the most effective ways to establish yourself as the benevolent leader of your dogs - most trainers and behaviorists are strongly opposed to free-feeding. With multiple dogs, it's hard to know when one dog is not eating, until it may be too late; as well, you don't always know when the dog last ate or how much, which can be problematic in the event there is an emergency and they need medical attention. At 14 weeks, the puppies should be eating 3-4 times a day; generally at around 6-8 months you can cut that down to twice a day.