U nedjelju obično ručamo s obitelji.

Because u + accusative is often used in Croatian for a time expression meaning on a particular day or on Sundays / on Sunday.

• nedjelja = Sunday
• u nedjelju = on Sunday

In this sentence, u nedjelju means on Sunday or, together with obično, on Sundays / usually on Sunday.

Croatian often uses u with days and parts of the day in time expressions:

• u ponedjeljak = on Monday
• ujutro = in the morning
• u večer / more commonly navečer = in the evening

So u nedjelju is the natural form here.

Nedjelju is the accusative singular of nedjelja.

The basic form is:

• nedjelja = Sunday

But after the preposition u when it means on a day/time point, Croatian uses the accusative:

• u nedjelju

This is a normal noun change:

• nominative: nedjelja
• accusative: nedjelju

So the ending changes because the preposition u requires that case in this meaning.

It can function as either, depending on context.

In this sentence, because of obično = usually, the whole sentence is understood as a habitual action:

• U nedjelju obično ručamo s obitelji.
• We usually have lunch with the family on Sundays.

Without obično, u nedjelju could also mean a specific upcoming or past Sunday:

• U nedjelju ručamo s obitelji.
• We’re having lunch with the family on Sunday.

So obično is what strongly gives it the repeated, habitual meaning here.

Obično means usually.

It tells you that the action is habitual, not a one-time event:

• ručamo = we have lunch / we are having lunch
• obično ručamo = we usually have lunch

It works much like English usually, although Croatian word order is more flexible. In this sentence, it naturally comes after the time phrase:

• U nedjelju obično ručamo s obitelji.

You could also hear slight variations in word order, such as:

• Obično u nedjelju ručamo s obitelji.
• U nedjelju ručamo s obitelji obično. (much less natural)

The version in your sentence is very natural.

Ručamo is the 1st person plural present tense of the verb ručati = to have lunch / to eat lunch.

So:

• ručam = I have lunch
• ručaš = you have lunch
• ruča = he/she/it has lunch
• ručamo = we have lunch
• ručate = you all / formal you have lunch
• ručaju = they have lunch

In this sentence, ručamo means we have lunch or we eat lunch.

Because Croatian often uses the present tense for habits, ručamo here is best understood as we usually have lunch.

Because Croatian usually does not need subject pronouns when the verb ending already shows who the subject is.

• ručamo already means we have lunch
• so mi ručamo is usually unnecessary

Croatian is a pro-drop language, which means pronouns like I, you, we, they are often omitted unless they are needed for emphasis or contrast.

So:

• Ručamo s obitelji. = We have lunch with the family.
• Mi ručamo s obitelji. = We have lunch with the family.
  This sounds more emphatic, like we do, maybe not someone else.

Both s and sa mean with, but sa is mainly used for easier pronunciation in certain sound combinations.

The usual form is s:

• s obitelji = with the family

Croatian often uses sa before words beginning with certain consonants or clusters, for example:

• sa mnom = with me
• sa sestrom can also be heard, depending on style and pronunciation comfort

But before a vowel, as in obitelji, s obitelji is completely normal and standard.

After s meaning with, Croatian uses the instrumental case.

So:

• obitelj = family
• s obitelji = with the family

The noun obitelj is one of those nouns whose form can look the same in more than one case, so learners often need to memorize it as part of a phrase:

• obitelj = family
• s obitelji = with family / with the family

The important grammar point is:

• s
  • instrumental = with

Because Croatian has no articles like English a/an/the.

So obitelj can mean:

• family
• the family
• sometimes even a family

The exact meaning depends on context.

In s obitelji, English naturally translates this as with the family or sometimes with family, depending on the situation.

This is a very common adjustment English speakers have to make: Croatian leaves out articles entirely.

Yes, very often it can be understood that way from context.

Croatian does not always state possession if it is obvious. So:

• s obitelji can mean with the family
• in many real-life contexts, that effectively means with my/our family

If you want to be explicit, you could say:

• s mojom obitelji = with my family
• s našom obitelji = with our family

But the shorter s obitelji is completely natural when the meaning is clear.

No, Croatian word order is fairly flexible, but some versions sound more natural than others depending on emphasis.

Your sentence:

• U nedjelju obično ručamo s obitelji.

This is a very natural neutral order:

1. time expression
2. adverb
3. verb
4. accompaniment phrase

Other possible orders include:

• Obično u nedjelju ručamo s obitelji.
• S obitelji obično ručamo u nedjelju.

These are grammatical, but they shift emphasis:

• starting with obično emphasizes the habitual nature
• starting with s obitelji emphasizes with whom

So the sentence order is not rigid, but the original version is a standard, natural choice.

Yes. Croatian present tense can cover both a simple present and a present continuous meaning, depending on context.

• Ručamo. can mean We have lunch or We are having lunch
• context tells you which one is meant

In your sentence, because of obično, it clearly means a repeated action:

• We usually have lunch with the family on Sundays

So although English uses usually have, Croatian simply uses the present tense ručamo.

Ručati specifically refers to having lunch or eating the midday meal.

It is more specific than the general verb:

• jesti = to eat

So:

• ručati = to have/eat lunch
• večerati = to have/eat dinner
• doručkovati = to have/eat breakfast

In this sentence, ručamo clearly refers to lunch, not eating in general.