One of the brands, Oxbow, has a website you can order from. Otherwise, we have some at our clinic. Some pet stores have a variety of brands, so just ask your veterinarian which brands you should go for and which you should avoid.

Guinea pigs eat hay, a lot of hay. They can eat pellets and certain veggies as well.

Guinea pigs are social creatures. So having them kind of in pairs is best if they're bonded. Otherwise, if you can be their bonded pair, they can get lonely because they are social creatures, so ensure they have enough interaction with you or their little buddies.

That can be a sign of boredom, just a stereotypical behavior. Make sure that they are getting out, getting their exercises, that they're stimulated enough, and they have enough enrichment. You want to be careful if they're biting their cage because, many times, cages are metal, and they can chip their teeth, so eliminate that as much as possible. Find toys or something else to distract them. You can hide their pellets around their enclosure, so they have to hunt for them.