Bilo da kum vozi ili ide taksijem, mora stići prije mladenke.

It means whether ... or ....

So:

• Bilo da kum vozi ili ide taksijem = Whether the best man drives or goes by taxi

This structure introduces two alternatives, but the result stays the same:

• ... mora stići prije mladenke = ... he has to arrive before the bride

It is a very common way to say no matter which of these two possibilities happens.

In this expression, bilo da is a fixed construction. It does not agree with kum.

Even though kum is masculine singular, you still say:

• bilo da ...

not something like bio da ...

So it is best to learn bilo da as one set phrase meaning whether.

Yes. Both patterns exist.

You can say:

• Bilo da kum vozi ili ide taksijem ...
• Bilo da kum vozi, bilo da ide taksijem ...

Both mean basically the same thing: whether the best man drives or goes by taxi.

The version with ili is often a bit more straightforward for learners, because it feels similar to English whether ... or ....

In a wedding context, kum usually means best man.

More broadly in Croatian, kum can also mean:

• godfather
• a wedding sponsor/witness
• an important ceremonial witness in church or family events

So kum is a culturally important word, and its exact translation depends on context. In this sentence, because of mladenke (the bride), best man is the natural meaning.

Croatian often uses the present tense for things in the future when the context already makes that clear.

Here the sentence is about what must happen in a wedding situation, but Croatian still says:

• vozi = drives / is driving
• ide = goes / is going
• mora stići = must arrive

This is normal. Croatian does not need a separate future form in every clause the way English often does.

Also, after bilo da, Croatian normally uses a finite verb form, not an infinitive.

Because the noun for the means of transport is in the instrumental case:

• taksi → taksijem

After verbs like ići when you mean by means of transport, Croatian often uses the instrumental:

• ići autom = to go by car
• ići autobusom = to go by bus
• ići vlakom = to go by train
• ići taksijem = to go by taxi

So taksijem answers the idea by what means?

They are related, but not identical.

• ide taksijem = he goes by taxi
  This focuses on the means of transport.

• u taksiju = in the taxi
  This focuses on the location.

So in this sentence, ide taksijem is the natural choice because the point is how he travels, not where he is sitting.

It can cover both ideas depending on context.

Here kum vozi most naturally means:

• the best man drives
• or the best man is driving

In practical English for this sentence, it usually means if the best man drives himself.

That contrasts nicely with:

• ide taksijem = goes by taxi

So the two alternatives are:

1. he drives
2. he takes a taxi

Mora stići is a very standard Croatian pattern:

• mora = must / has to
• stići = to arrive

So literally: must arrive

After modal verbs like morati, Croatian commonly uses the infinitive:

• moram ići = I have to go
• mora doći = he/she has to come
• mora stići = he/she has to arrive

Here stići is a very good choice because it emphasizes arriving in time / reaching the destination, which fits the idea of getting there before the bride.

Because prije requires the genitive case.

So:

• mladenka = nominative singular
• mladenke = genitive singular

That is why you get:

• prije mladenke = before the bride

This is something worth memorizing:

• prije + genitive

For example:

• prije ceremonije = before the ceremony
• prije ručka = before lunch
• prije mladenke = before the bride

Formally, mladenke can look like either:

• genitive singular of mladenka
• or nominative plural

But after prije, the genitive is required, so here it must be:

• genitive singular = of/before the bride

The preposition tells you the case, and that tells you the meaning.

Croatian often drops subject pronouns when the verb form already makes the subject clear.

So instead of saying:

• ... on mora stići ...

it is completely normal to say just:

• ... mora stići ...

The subject is understood from the context: it is still kum.

This is very common in Croatian. English usually needs the pronoun, but Croatian often does not.

Because the first part is a subordinate clause:

• Bilo da kum vozi ili ide taksijem

and then the main clause follows:

• mora stići prije mladenke

Croatian normally separates that kind of introductory clause with a comma. So the comma is standard punctuation here.

Yes, Croatian word order is fairly flexible, though some versions sound more natural than others.

For example, you could also hear things like:

• Kum mora stići prije mladenke, bilo da vozi ili ide taksijem.

That still means the same thing.

However, the original order is very natural because it presents the two alternatives first, then gives the result:

• whether he drives or takes a taxi, he must arrive before the bride