Miaj gefratoj kaj mi kutime alportas fruktojn, kiam ni vizitas la geavojn.

Because mia is an adjective-like possessive, and in Esperanto adjectives agree with the noun they describe.

• mia frato = my brother
• miaj gefratoj = my siblings / my brothers and sisters

Since gefratoj is plural, mia becomes miaj.
If it were also a direct object, it would become miajn.

The prefix ge- shows a group containing both sexes together.

So:

• fratoj = brothers
• gefratoj = brothers and sisters together, often translated as siblings
• avoj = grandfathers
• geavoj = grandfather and grandmother together, meaning grandparents

In this sentence:

• miaj gefratoj = my siblings
• la geavoj = the grandparents

Both are grammatically possible, but Miaj gefratoj kaj mi is very natural because speakers often mention themselves last out of politeness.

So this is similar to English preferring:

• My siblings and I rather than
• I and my siblings

It is more a matter of style than grammar.

Kutime means usually. It tells you that this is a habitual action, not a one-time event.

In Esperanto, adverbs like kutime can often move around fairly freely, as long as the meaning stays clear. For example:

• Miaj gefratoj kaj mi kutime alportas fruktojn...
• Kutime miaj gefratoj kaj mi alportas fruktojn...

Both are fine. The version in the sentence is very natural.

The basic verb porti means to carry or to bear.
With the prefix al-, it becomes alporti, which means to bring, literally to carry to.

So:

• porti = carry
• alporti = bring

That fits this sentence well, because the fruit is being brought to the grandparents.

Because it is both:

• plural → -j
• a direct object → -n

So:

• frukto = a fruit
• fruktoj = fruits
• fruktojn = fruits as the direct object

Here, the thing being brought is the fruit, so fruktojn needs the accusative -n.

In Esperanto, viziti takes a direct object. You visit someone, not visit to someone.

So:

• Mi vizitas mian amikon. = I visit my friend.
• Ni vizitas la geavojn. = We visit the grandparents.

Because la geavojn is the direct object of vizitas, it takes -n.

A native English speaker may expect a preposition because some languages use one, but Esperanto does not here.

Because la means the, and it marks something definite or already identifiable.

• la geavojn = the grandparents, a specific known pair
• fruktojn = fruit / some fruit, not a specific previously identified set

So the sentence is talking about:

• a specific group of people: the grandparents
• an indefinite thing being brought: fruit

If you wanted to talk about specific fruit already known from context, you could say la fruktojn.

Yes, that is possible.

• la geavojn = the grandparents
• niajn geavojn = our grandparents

In this sentence, la geavojn is enough because the context already makes it clear whose grandparents they are: the ones connected with my siblings and I.

Using niajn geavojn would make the relationship more explicit, but it is not necessary.

Literally, kiam means when.
But in a sentence with kutime, it often has the sense of whenever.

So this sentence means something like:

• My siblings and I usually bring fruit when we visit the grandparents
• or more naturally in some contexts:
• My siblings and I usually bring fruit whenever we visit the grandparents

The habitual meaning comes from kutime.

Because Esperanto uses the present tense for habitual or repeated actions, just like English often does.

So:

• alportas = bring / are bringing
• vizitas = visit / are visiting

With kutime, the meaning is clearly habitual:

• we usually bring fruit
• when we visit

There is no need for a special tense here.

Because kiam ni vizitas la geavojn is a subordinate clause, and in Esperanto such clauses are usually separated with a comma.

So the comma helps show the structure:

• main clause: Miaj gefratoj kaj mi kutime alportas fruktojn
• subordinate clause: kiam ni vizitas la geavojn

This punctuation is standard and helpful for clarity.

Often yes in translation, but not perfectly in structure.

Gefratoj literally means brothers and sisters together. In English, the natural one-word translation is usually siblings.

So in this sentence, translating miaj gefratoj as my siblings is very natural.
Just remember that Esperanto is building the idea with:

• fratoj = brothers
• ge- = both sexes together

So the word is formed differently, even if the English translation is simple.