[akstrohm]

I would not ever expect the cats to be friends with the guinea pigs. Cats are predators and pigs are prey. A cat could seriously injure or kill a guinea pig, so do not allow them to be together. This will be very stressful for the pigs, and even under supervision, you might not be able to prevent an attack.

There is an entire section in this forum under the prefix litter training.

If you post your location, maybe someone in your area can refer you to a good vet. If you can't find one, be sure you are familiar with dangerous antibiotics and other general health info. Guinea Lynx has a lot of good information.