I think your are
the five fingers of a hand
My 1st brother is a bother, and points everything out
The index is used to point at something
My 2nd brother is tall, and quite foul at heart.
The middle finger is usually the longest
(sorry, as a non-native speaker, I did not understand "foul at heart", is that an idiom?)
My 3rd brother is about as tall as my 1st, and quite decorative.
The ring finger is often as long as the index and carry all sorts of rings
My 4th brother is short and skinny, but among the strongest of us all.
The thumb is the shortest but the strongest of all five
I am short and squat and weak, but am by far the most useful.
You are pinky, the most useful for you owner's ears
Update: below are some corrections by the OP to my initial answer.
The 4th brother is the pinky, short and skinny, but among three of the strongest fingers of the hand. The narrator is the thumb, short and squat, but most useful because the opposing thumb allows us to grasp things.