While I can translate the phrase literally, the meaning of the original phrase, "your cats are twenty" is confusing. Are they twenty years old? Then the translation would be different, I suppose. And besides, it is an unlikely age for a cat.
No one really says "Your cats are twenty". It might be interpreted to mean that your cats are 20 years old. Usually we say "You have twenty cats" or in a more archaic way, "Your cats are twenty in number".