If you find the other cats there to be cuter than we are, don't come back here anymore!
If you think the other cats are cuter than us, you've got no business coming back home!
ご質問ありがとうございます。
① "If you find the other cats there to be cuter than we are,"＝「そこにいる他の猫たちが僕たち（私たち）よりも可愛いと思うのなら」
"don't come back here anymore!"＝「もうここに戻ってくるな！」
② "If you think the other cats are cuter than us,"＝「他の猫たちが僕たち（私たち）よりも可愛いと思うなら」
"you've got no business coming back home!"＝「君が家に帰ってくる権利は無い！」
ご参考に。
アメリカ合衆国 
