Брат и сестра иногда ругаются из‑за мелочей, но потом быстро мирятся.

Because the subject is Брат и сестра — brother and sister — which refers to two people. In Russian, a compound subject like this takes a plural verb, just like in English:

• Брат и сестра ругаются
• The brother and sister argue

So both verbs are in 3rd person plural: they argue, they make up.

The ending -ся makes the verbs reflexive in form, but that does not always mean someone literally does something to themselves. Very often in Russian, -ся verbs describe:

• mutual actions
• states
• intransitive meanings

Here both verbs are naturally used this way:

• ругаться = to quarrel / argue
• мириться = to make up / reconcile

In this sentence, -ся suggests a two-way interaction between the brother and sister.

This is a very common question.

• ругать usually means to scold someone, to tell someone off
• ругаться often means to argue, to quarrel, or sometimes to use bad language

So here:

• Они ругаются = They are arguing / quarreling

If you said Брат ругает сестру, that would mean The brother is scolding his sister, which is a different idea.

After из-за, Russian normally uses the genitive case.

The noun here is мелочь = a small thing / trifle.
Its plural is мелочи, and the genitive plural is мелочей.

So:

• из-за мелочей = because of trifles / over small things

That is why you do not see мелочи here.

In this sentence, из-за means because of or over.

So ругаются из-за мелочей means they quarrel over small things.

A useful note: из-за can also mean from behind in other contexts, depending on the sentence. For example:

• из-за дома = from behind the house

But here the meaning is clearly because of / over.

Because that is simply the standard spelling of this preposition: из-за.

It is a fixed form, and you should learn it as one unit. Russian has a few prepositions and particles written with a hyphen, and this is one of the common ones.

Because Russian present tense is often used for habitual or repeated actions, just like English present simple.

Here the key word is иногда = sometimes, which shows that this is a general pattern:

• they sometimes argue
• then they quickly make up

So the sentence is not about one specific argument happening right now. It describes what usually happens.

Both are imperfective verbs:

• ругаться
• мириться

That makes sense because the sentence describes repeated, habitual behavior, not one completed event.

Russian perfective verbs do not have a true present-tense meaning like this. If you wanted to talk about one completed future reconciliation, you might use помирятся instead:

• Потом они помирятся = Then they will make up

But in the original sentence, the imperfective forms are correct because the meaning is habitual: this happens sometimes.

This is mostly an aspect difference:

• мириться = imperfective, focusing on the process or repeated action of making peace
• помириться = perfective, focusing on a completed reconciliation

In your sentence, мирятся works well because the whole statement describes a recurring pattern.

Compare:

• Они быстро мирятся = They make up quickly / They tend to make up quickly
• Они быстро помирились = They made up quickly (one completed event in the past)

Because но means but, and it joins two clauses:

• Брат и сестра иногда ругаются из-за мелочей
• но потом быстро мирятся

In Russian, a comma is normally placed before но when it connects two clauses, just as English often uses a comma before but.

Yes. Russian word order is more flexible than English word order, although some versions sound more natural than others.

The original order is very natural:

• Брат и сестра иногда ругаются из-за мелочей, но потом быстро мирятся.

You could move adverbs around for emphasis, for example:

• Брат и сестра ругаются иногда из-за мелочей, но быстро потом мирятся.

But that sounds less neutral. The original sentence is the most natural everyday phrasing.

In general:

• иногда naturally goes near the verb
• потом sets the sequence
• быстро modifies мирятся

Russian has no articles like a or the, so брат и сестра can mean either, depending on context.

Without more context, English might translate it as:

• Brother and sister
• A brother and sister
• The brother and sister

Russian leaves that choice to the situation or the broader context.

A learner will often want the stress here:

• руга́ются
• ми́рятся
• мелоче́й

A rough pronunciation guide:

• руга́ются ≈ roo-GA-yut-sa
• ми́рятся ≈ MEE-ryat-sa
• мелоче́й ≈ mye-la-CHEY

The exact sounds are not identical to English, but knowing the stress is very helpful, because Russian stress is unpredictable and can change from form to form.