Хотя киви и манго были дорогими, я всё же купил их для смузи.

Хотя means although / even though and introduces a concessive subordinate clause.

So the structure is:

Хотя киви и манго были дорогими, ...
= Although kiwi and mango were expensive, ...

In Russian, subordinate clauses are separated by a comma, so the comma comes before the main clause:

Хотя ..., я всё же купил ...

Because both киви and манго are indeclinable borrowed nouns in standard Russian. That means their form usually stays the same instead of taking different case endings.

So Russian shows their role in the sentence through:

• word order and context
• agreement on other words, such as verbs and adjectives

Here they are the subject of the clause, but the nouns themselves still stay киви and манго.

Because киви и манго is a compound subject: two nouns joined by и. In Russian, that normally takes a plural verb.

So:

• киви было дорогим = the kiwi was expensive
• манго было дорогим = the mango was expensive
• киви и манго были дорогими = the kiwi and the mango were expensive

Even though each noun by itself is usually treated as singular, together they make a plural subject.

Дорогими is the instrumental plural form of the full adjective дорогой.

After past-tense быть, Russian often uses:

• a full adjective in the instrumental: были дорогими
• or a short adjective: были дороги

So both of these are possible:

• киви и манго были дорогими
• киви и манго были дороги

The version with дорогими sounds very natural and neutral here.

Дорогие is less standard in this kind of predicate use after были. A learner is safest using дорогими here.

Всё же means something like:

• still
• nevertheless
• all the same

It emphasizes that the speaker bought them despite the fact that they were expensive.

So:

• я купил их = I bought them
• я всё же купил их = I bought them anyway / I still bought them

The sentence would still be grammatical without всё же, but the contrast would be weaker.

Купил is perfective, so it presents the action as a completed result: the speaker ended up buying them.

That fits this sentence well:

• they were expensive
• but in the end he bought them

Покупал is imperfective and would usually suggest:

• process
• repeated action
• background information

So купил is the natural choice for I bought them as a single completed action.

Их is the accusative plural form of the pronoun они in this sentence.

It is the direct object of купил:

• купил кого? что?
• их

It refers back to киви и манго.

For this pronoun, the accusative plural form is их, which is the same in form as the genitive plural.

The preposition для means for and requires the genitive case.

So grammatically, смузи here is in the genitive after для.

But смузи is also an indeclinable borrowed noun, so its form does not change. That is why you still see смузи, not a different ending.

So:

• для
  • genitive
• смузи is genitive here
• but the form stays смузи

It can be understood either way depending on context.

Russian has:

• no articles
• many indeclinable nouns whose singular and plural look the same

So для смузи could mean:

• for a smoothie
• for smoothies
• for making smoothie(s) in a general sense

In this sentence, the most natural English translation is probably for a smoothie or for smoothies, depending on the situation.

In standard Russian, these indeclinable inanimate nouns are usually treated as neuter when singular.

For example:

• спелое киви
• сладкое манго
• вкусное смузи

In your sentence, you do not see neuter singular agreement because:

• киви and манго are joined by и
• that creates a plural subject
• so the sentence uses были дорогими

Yes. Russian word order is fairly flexible.

For example, you could also say:

Я всё же купил их для смузи, хотя киви и манго были дорогими.

That means the same thing, but the emphasis changes slightly:

• the original sentence starts with the although part
• this version starts with the main action

The original order is very natural because it sets up the contrast first and then gives the result.