YOU SAID:
My brother has a cat who has a cat who has a cat who has a cat who has a cat who has a dog.
INTO JAPANESE
私の兄は、犬を飼っている猫を飼っている猫を飼っている猫を飼っている猫を飼っています。
BACK INTO ENGLISH
My brother has a cat that has a cat that has a dog. My brother has a cat that has a cat that has a dog.
INTO JAPANESE
私の兄は犬を飼っている猫を飼っている猫を飼っています。私の兄は犬を飼っている猫を飼っている猫を飼っています。
BACK INTO ENGLISH
My brother has a cat that has a dog and a cat that has a dog. My brother has a cat that has a dog and a cat that has a dog.
INTO JAPANESE
私の兄は犬を飼っている猫と犬を飼っている猫を飼っています。私の兄は犬を飼っている猫と犬を飼っている猫を飼っています。
BACK INTO ENGLISH
My brother has a cat that has a dog and a cat that has a dog. My brother has a cat that has a dog and a cat that has a dog.
That didn't even make that much sense in English.