New Pups!

What breed(s) are the puppies? Also, Purina makes quite a few different brands, so what brand were they on? And what adult brand and recipe are you switching them to?

As a side note, make sure to read up on littermate syndrome. It's generally inadvisable to adopt two puppies of the same age at the same time (whether they're littermates or not). The puppies can bond more closely to each other than they do with their human family, which makes them more distant and antisocial. It also means that you'll have to spend three times the amount of time you usually would with your socialization and training schedules, as each puppy needs to be trained separately, socialized separately and then trained and socialized together. They should be crated apart from each other at night and fed apart during the day. Littermate syndrome is no joke and can lead to you ending up with a pair of antisocial dogs who prefer each other's company to humans, and who will have very bad anxiety if they ever need to be separated.

The two greatest weapons to combat littermate syndrome are knowledge and time, so it sounds like you are well prepared to make sure your pups grow into healthy and stable adults.

The protein myth has been disproved. High protein diets do not cause bone growth issues. A study by veterinarians at Michigan State University discovered that calcium and phosphorous were the two culprits in improper bone growth. It is usually more of a problem with giant breed puppies (I have Danes, which is why I'm aware of this), but it can effect large breed puppies as well. The appropriate amounts are:

Calcium - 1-1.5%
Phosphorous - .08-1%

I'd try to stay in the middle of those ranges, and be aware of whether the food you're feeding says 'max' or 'min'. If the calcium is 1.5% MIN, for instance, I'd probably avoid feeding that particular recipe.

You also need to keep the puppy who is knuckling off of slippery floors. Carpet only. Carry him/her up and down stairs until the knuckling resolves. Limit play time to prevent stress on the forelegs.

This website has some good information about how to wrap a puppy who is knuckling: http://www.greatdanelady.com/articles/knuckling_over.htm

It also contains some outdated information, as the Great Dane Lady passed away in 2004, I believe. Therefore the dietary information concerning calories and protein has since been disproved by numerous studies published by renowned veterinary institutions. However, the wrapping information is still good to follow if the knuckling is severe. I'd suggest that you have a vet teach you how to wrap the first time around, and be careful with using vet wrap, as it constricts and can tighten drastically, meaning that even if you put it and it feels loose, it can end up cutting off circulation.