"Those are their drinks."
Translation:Itu minuman mereka.
The modifier almost always comes after the noun in Indonesian. :) If it helps, you might need to imagine adalah is there (this is the copula but it is a bit formal or used to define things)
(Itu) adalah (minuman mereka)
The itu heading the sentence is the subject, while anything following it will be another noun or a verb.
Another example might be itu kucing mereka That is a cat that is theirs Itu anjing hitam That is a dog that is black
I usually think of all adjectives in this way to translate it quicker.
It's mostly a matter of getting used to having modifiers follow the nouns!