Translation:Their older brother is short.
It isn't, but there's a rather important tone rule regarding two consecutive 3rd tones. When you have 2 consecutive 3rd tones - i.e. 很矮 - you pronounce the first with a 2nd tone. Ergo, 很矮 becomes hén-矮.
I don't mean to say that the audio here is perfect, but to enlongate the pronunciation into literally "很" "矮" would still be incorrect.
I think you can omit "elder" or "younger" when translating into English because we tell "哥哥" and "弟弟" whenever the age is known, not just for emphasis. "兄弟" is rather not common to refer to your family.
And according to my experiences, if you really forgot whether it is "哥哥" or "弟弟" of someone, you'd rather ask first, but not just use "兄弟." This is cultural thing.
This question keeps getting lost in the madness so I'll ask it again hoping to get a native speaker's response. Not too far back and again in the preface of this lesson, we are taught that 很 does not necessarily men very. It is even said , more or less, that most times you see it it will not mean 'very' so why is "My older brother is short" incorrect here?
It's not grammatically incorrect to leave out 很 but it is stylistically incorrect. It sounds very wrong to almost everyone to leave out the adverb but it's not strictly required. For example "你矮" as a sentence by itself grammatically is ok and Chinese people will say that, but they will also say it sounds VERY weird.
While Chinese distinguishes between older and younger brothers and sisters, note that cousins and even friends can also be called “brothers” or “sisters,” especially 哥哥 and 姐姐. Also, 帅哥 means a "handsome man," often not one's real brother, while 空姐 means "stewardess." (The literal translation of the unisex "flight attendant" is rare in Chinese because they are usually young women in China, as in many other Asian countries.)
You don't use 是 when the phrase describes a quality with an adjective, instead you put 很 to connect the adjective instead of the verb "to be", like you do in English. The adjective basically is the predicate of the sentence without the verb. This is explained in the Tips and notes of the Greetings 2 section.