Breakdown of Речь идёт о моих братьях.
брат
brother
мой
my (мой, моя, моё) / mine
о
about (о, об, обо)
идти
to go (on foot) / to proceed, go (of a process)
Questions & Answers about Речь идёт о моих братьях.
Why is the verb of motion идёт used here to mean "is about"?
This is a highly common metaphorical use of the unidirectional verb идти (to go). The idiom речь идёт о literally means "the speech goes about," but it is the standard Russian way to express "the conversation is about," "the issue concerns," or "it is a matter of."
Could I use the multidirectional verb ходит instead of идёт in this context?
No, you cannot say речь ходит. Idioms and metaphorical uses of verbs of motion almost always lock into one specific verb. To express what a conversation or text is about, Russian strictly uses the unidirectional идёт.
How would this metaphor look in the past or future tense?
The metaphor remains exactly the same, but the verb changes tense. For the past, you use the past tense of идти, which is шла because речь is feminine: Речь шла о моих братьях. For the future, you typically use the perfective prefix по-: Речь пойдёт о моих братьях.
I remember the word брат has an irregular plural. Is that why it becomes братьях here?