Mimi ninamwamini dada yangu.

It is one verb word made of several parts:

• ni- = I
• -na- = present tense
• -mw- = him/her for a singular person
• -amini = trust / believe

So ninamwamini means I trust him/her or I believe him/her. In this sentence, -mw- refers to dada yangu.

Because Mimi is the independent pronoun, while ni- is the subject marker built into the verb.

In Swahili, the subject is usually already clear from the verb, so Mimi is often optional. Here it adds emphasis or contrast, something like:

• As for me, I trust my sister
• I trust my sister

A more neutral version would simply be Ninamwamini dada yangu.

Yes, they both refer to the same object, and that is normal in Swahili.

With a specific human object, Swahili very often uses an object marker inside the verb and still says the full noun phrase after the verb. So:

• -mw- points to her
• dada yangu tells you exactly who her is

This is especially common and natural with people.

The object marker is basically m- for a singular person, but before a vowel it becomes mw- for easier pronunciation.

Since -amini begins with a, you get:

• m- + amini -> mwamini

So ninamwamini is the expected form.

Words like dada, kaka, mama, and baba belong to a special group in Swahili.

Even though they refer to people and often take person agreement in verbs, their possessives usually use forms like:

• yangu = my
• yako = your
• yake = his/her

So you say:

• dada yangu = my sister
• mama yangu = my mother
• baba yangu = my father

But with a regular class 1 noun such as mtoto, you get:

• mtoto wangu = my child

-na- is the usual present tense marker.

Depending on context, it can correspond to English:

• I trust
• I am trusting

Swahili does not always separate those two meanings as strictly as English does.

It can mean either, depending on context.

• With a person, it often means trust or believe someone
• With an idea, claim, or statement, it often means believe

So in this sentence, trust is the most natural English translation.

Not by itself. -mw- means him or her for one person.

Swahili object markers do not show gender here. You understand it as her only because the noun dada tells you the person is female.

The basic order is:

• Mimi = subject
• ninamwamini = verb
• dada yangu = object

So the neutral pattern is subject + verb + object.

Because Swahili puts a lot of information inside the verb, the order can sometimes change for emphasis, but the sentence you have is a normal straightforward order.

Yes, if the listener already knows who -mw- refers to.

Then Mimi ninamwamini would mean I trust him/her. Adding dada yangu makes the reference explicit: my sister.

A simple guide is:

MEE-mee nee-na-mwa-MEE-nee DA-da YA-ngu

Helpful points:

• Swahili usually stresses the second-to-last syllable
• mw is pronounced together
• In yangu, ng sounds like the ng in finger

Syllables:

• Mi-mi
• ni-na-mwa-mi-ni
• da-da
• ya-ngu