Now would be about right. Just soften the food with warm water, and mush it up. You can add a bit of goat's milk to it (this is just what I do). Your Mama will be needing exta food too, so make sure she's getting a real good high quality food as well. You can feed them large breed puppy, but I have heard different opinions on this. I would consult another Bully breeder.
I've never used Diamond, but I know people who are using it.If the dogs are looking healthy, and this is the food that fits into your budget, then it will do. I think you are going to get a lot of poop though, and if I remember correctly, Diamond has corn in one of their foods, which I'm not a big fan of.