Hi there! Welcome to the forum and congratulations on your new piggies!
Most pet store cages really are much too small. Even though they are called "large" or "extra large," they are really nothing more than a litter box. I highly encourage you to build a C&C cage for all of your guinea pigs, as a C&C cage is honestly the best thing you could do for your guinea pig, next to proper diet and a same-sex cagemate.
Have you visited
Guinea Lynx? It's a great resource for all sorts of care information, including
feeding,
exercise, and
health.
As others have said, there are pretty much two best brands of food and hay for guinea pigs. The best of the best is (broken link removed), which has extremely high quality pellets and hay. All guinea pigs need several heaping handfuls of grass hay and small amounts (about 1/4 cup) pellets daily, as well as about one cup of mixed
vegetables per guinea pig daily.
Guinea pigs under six months of age need a little extra calcium in their diet. You will want to feed plenty of grass hay as the main part of the diet (try hays like Timothy or orchard grass). You will also need to supplement with small amounts of alfalfa to provide that extra calcium. You can feed alfalfa-based pellets, but timothy-based pellets won't hurt, either. KMS has a great (broken link removed) that would be perfect for your young guinea pigs since they are under six months of age. Otherwise, you can feed timothy hay or orchard grass hay (same unlimited amount daily) plus a few small handfuls of alfalfa daily. Oxbow, which is the next best thing, has both (broken link removed)and (broken link removed). You can also try looking for a
local hay farm to find hay near you. When you buy hay locally, you'll want to look for hay that is soft, pliable (you can bend and twist it easily), fresh, green, and good-smelling. For pellets, KMS's (broken link removed) or (broken link removed)are great choices; or, Oxbow's (broken link removed)or (broken link removed).
Once your guinea pigs get to six months of age, you need to switch to a low-calcium diet - that means grass hay only (timothy or orchard grass) and Timothy-based pellets in addition to the one cup of vegetables.
I know that's kind of a lot to digest, but you'll catch on soon!
Good luck!