I believe the answer should be C. This is because an appositive phrase is a part of the sentence that renames another noun in some way. So if I say "My lily, the gigantic flower in my backyard, has stopped growing." then I can look and see that the part saying "the gigantic flower in my backyard" has just rephrased the part "My lily", and the same applies to your sentence. The part saying "the ones with the calico fur" just restates the part "Our cats".
I hope I helped! And if you need more information, please tell me, and I'll fix it! :D
