You are a hero to take a dog on like this is comendable! There is nothing wrong with a little bit of Pedigree puppy, i can name many worse brands than this Iams, Hills Science...... ect, My advice is to try intergrating some Advance puppy food as this is IMO the best dryfood on the market for puppys, by far. My puppies have thrived on this and we have had exceptional results.
I hope you can get your pup to eat but i do agree if they won't eat it take it away from them and try it agian later they will eat when they figure out that you won't give in! ok Good luck.
JB