If your animals have been kept indoors until now, I would keep them indoors until at least the spring. They will not have developed a warm enough winter fur.
It is not a good idea to keep a rabbit and a guinea pig in the same cage. Sometimes they can become best friends, but their behaviour is very different, and it can happen that the rabbit injures the guinea pig. Does your rabbit hump the guinea pig a lot? Is the guinea pig a boy, too? I would definitely get them both neutered, and if you see any signs of fighting, keep them in separate cages.
Hope that helps.