the/an older brother of Jack)

[NAL123]

Suppose Jack has three older brothers, and John and Mike are friends of Jack. Chris is Jack's second oldest brother.

[John doesn't know anything about Jack's siblings]

1) Chris to John on the phone: Hi John! I'm Chris, Jack's older brother (or, the older brother of Jack)....

The next day:

2) John to Mike: yesterday Jack's older brother (or, the older brother of Jack), Chris, called me to ask if Jack was with me.

Is the use of the article "the" correct in (1) and (2)? Or should it be "an older brother"?

 

[5jj]

Most speakers of BrE have no interest in such things. More likely dialogues would be:

1) Chris to John on the phone: Hi John! This is Chris, Jack's brother ...

2) John to Mike: yesterday Jack's brother Chris called me to ask if Jack was with me.

 

[Skrej]

If it's really necessary to clarify (and it's likely not), then use "Jack's older brother" (no articles). However, if all three brothers are older, it's still not going to establish a birth order.

Only 'oldest' would give any degree of certainty, but of course only one of the three can use that.

 

[probus]

Note that @NAL123's native language is Hindi. Hindi uses different words for older brother and younger brother.