U našoj obitelji je običaj da nedjeljom pijemo kavu zajedno.

Because u means in here, and when u expresses location, it takes the locative case.

• obitelj = family
• u obitelji = in the family
• našoj agrees with obitelji in gender, number, and case

So:

• naša obitelj = our family
• u našoj obitelji = in our family

Since obitelj is feminine singular, the adjective becomes našoj in the locative singular.

Good question. Some Croatian nouns do not change much in certain cases.

For obitelj, the form obitelji can be:

• genitive singular
• locative singular
• dative singular

So even though it looks like the basic form to a learner, it is actually a case form here. The preposition u tells you that this is the locative meaning: in our family.

Literally, je običaj means is a custom or is the custom.

In this sentence, običaj is being used in a very natural Croatian way to express something habitual or traditional:

• U našoj obitelji je običaj... = In our family, it is customary...
• more literally: In our family, it is a custom...

So običaj does not just mean a formal tradition; it can also mean a regular family habit.

Both are possible in Croatian, but je is a clitic, and clitics usually go in the second position of the sentence or clause.

So in:

• U našoj obitelji je običaj...

the whole opening phrase U našoj obitelji counts as the first element, and je comes right after it.

A more English-like word order such as U našoj obitelji običaj je... is possible in some contexts, but it is less neutral here. The given sentence sounds natural and standard.

After nouns like običaj, Croatian very often uses da + present tense to express what people usually do.

So:

• običaj da pijemo kavu = the custom of drinking coffee
• more naturally: the custom that we drink coffee

English would often prefer an infinitive or -ing form, but Croatian commonly uses da + present.

This structure is very common:

• Običaj je da... = It is customary that...
• Normalno je da... = It is normal that...
• Važno je da... = It is important that...

So da pijemo is completely natural here.

In Croatian, the present tense is regularly used for habitual actions, just like in English:

• We drink coffee on Sundays
• Nedjeljom pijemo kavu

The present tense does not only mean right now. It can also describe something that happens regularly, generally, or as a custom.

So pijemo here means we drink / we usually drink.

Because piti is imperfective, and that is usually the better choice for a repeated, habitual action.

• piti / pijemo = to drink / we drink
• popiti / popijemo = to drink up, to finish drinking

In this sentence, the focus is on a regular habit, not on a completed result. So pijemo kavu sounds natural.

If you used popijemo, it would sound more like we finish a coffee, which is not the main idea here.

Nedjeljom is the instrumental singular of nedjelja.

Here the instrumental is used adverbially to express a repeated time:

• nedjeljom = on Sundays, on Sundays in general

This is a very common Croatian pattern:

• ponedjeljkom = on Mondays
• utorkom = on Tuesdays
• subotom = on Saturdays
• nedjeljom = on Sundays

So this is not about one specific Sunday; it means a habitual time.

This is an important distinction:

• nedjeljom = on Sundays, meaning regularly / every Sunday / Sundays in general
• u nedjelju = on Sunday, meaning one specific upcoming or mentioned Sunday

Examples:

• Nedjeljom pijemo kavu zajedno. = We drink coffee together on Sundays.
• U nedjelju pijemo kavu zajedno. = We are drinking coffee together on Sunday.

So the sentence uses nedjeljom because it describes a family habit.

Because kava is the direct object of pijemo, and direct objects usually go in the accusative case.

• kava = coffee
• pijemo kavu = we drink coffee

So:

• nominative: kava
• accusative: kavu

This is a very common pattern with verbs like piti, jesti, kupiti, voljeti, etc.

Croatian often omits subject pronouns when they are already clear from the verb ending.

• pijemo already means we drink
• the ending -mo tells you the subject is we

So adding mi is usually unnecessary unless you want emphasis:

• Mi pijemo kavu zajedno. = We drink coffee together.
  (emphatic, contrastive)

In a neutral sentence, pijemo by itself is enough.

Zajedno means together.

It modifies the action pijemo kavu:

• pijemo kavu zajedno = we drink coffee together

Its position is fairly flexible. For example, these are all possible:

• ... da nedjeljom pijemo kavu zajedno
• ... da zajedno pijemo kavu nedjeljom
• ... da pijemo zajedno kavu nedjeljom

The version in your sentence sounds natural and neutral. Croatian word order is flexible, but different placements can slightly change emphasis.

Yes. Croatian word order is much more flexible than English word order because case endings show grammatical relationships.

For example, you could also hear:

• U našoj obitelji običaj je da nedjeljom pijemo kavu zajedno.
• Običaj je u našoj obitelji da nedjeljom pijemo kavu zajedno.
• Nedjeljom je u našoj obitelji običaj da pijemo kavu zajedno.

These versions are all understandable, but the original sentence sounds very natural and balanced. Changes in word order usually affect focus or emphasis, not the basic meaning.

No. Croatian also has porodica, but obitelj is the more standard and common neutral word in Croatian, especially in Croatia.

So:

• obitelj = family
• u našoj obitelji = in our family

In many learning materials, obitelj is the word you will see most often.

It is neutral standard Croatian.

Nothing in it is especially formal or casual. You could say it in normal conversation, write it in a textbook, or use it in everyday speech.

That makes it a very useful model sentence for learners because it shows several common Croatian patterns:

• u + locative
• je in second position
• običaj da + present
• instrumental for repeated time (nedjeljom)
• omitted subject pronoun
• accusative direct object (kavu)