You can still see my boxers ribs.?

I have a pair of boxer pups, i got them at 8weeks old they are now 4mos. old.I feed them 3x a day pedigree puppy chow, when they eat 2cups per meal they are done in 60sec.you can still see there ribs, whats up with that? they have been wormed for all inc. tape worms.They have lots of energy and are very sweet, and there s are bony looking.I did not buy them from a good breeder,the owners were not very clean people.I need some expert advice . linda