I'll try to answer what questions I remember. I'm a newbie owner too, only a couple months, but I've picked up on things fast. Fleece is the best alternative that you can use that would be the cleanest for you. People have mentioned that, if you can't find fleece locally than you can get fleece from
Search Galena Bay Novelty Fabrics web store (not a big selection) or check out ebays international site
eBay - Deals on new and used electronics, clothing, collectables and more on eBay where you can find fleece bty and fleece blankets, most of which should be able to be shipped to Brazil. I've purchased many things from Israel and even India, so the internet is great for that. Also, if you're worried about the males fighting (I don't have males but have read this) some people make a cage with a divider (almost like two cages) and that way they can interact without fighting. You could do this with your rabbits as well. Wire shelves are a good alternative as well to the normal grids used in C&C cages. Also, we used a roofing material on the bottom of our cage because no one had coroplast around here in big sheets. Don't ask me why, but we called everywhere and they only had small sheets they wanted to charge so much for, but we found a mold proof/water proof/roofing material that has worked great for us so far.
Also, your cats may or may not like the guinea pigs some day but they will eventually lose the novelty of them and get over them. I've had cats most my life except recently and had hampsters, birds, lizards, etc. with my cats as well and it's always a novelty when you first get them. If you didn't get the guinea pig while the cats were kittens though, they will most likely never be able to be "friendly" with your piggie. I hope that helps. I worked as a vet tech for a while before I got pregnant with my son so I know a little on animal behaviour as well as the gobs of animals I've had in my life (a bit of a facination for me, animal behaviour). I also know the vet situation too. I live in an area where not one vet knows how to handle guinea pigs. I have one local vet that will take them in an emergency, but I have to drive an hour to an hour and half just for a checkup.
Anna