No wonder no one has answered your question what's it supposed to mean and you have spelt mammals wrong too a five year old could spell that learn to wright!
mammles isn't a word, but the word Mammals means: -noun any vertebrate of the class Mammalia, having the body more or less covered with hair, nourishing the young with milk from the mammary glands,...
i think, it will be; "both of them are" since both means at least 2. so we are talking about double, and both takes plurals. as a result:=> both of them are...