Marináda a grilovací omáčka jsou hotové.

Because the subject is two things together: marináda a grilovací omáčka = the marinade and the barbecue sauce.

In Czech, when two singular nouns are joined by a (and), they usually make a plural subject, so the verb is plural too:

• Marináda je hotová. = The marinade is ready.
• Omáčka je hotová. = The sauce is ready.
• Marináda a omáčka jsou hotové. = The marinade and the sauce are ready.

So jsou is the correct plural form of být (to be) here.

Because hotové agrees with the whole subject, not with just one noun.

Both marináda and omáčka are feminine singular, but together they form a feminine plural subject. The adjective therefore also goes into the plural:

• hotová = feminine singular
• hotové = feminine plural

So:

• Marináda je hotová.
• Omáčka je hotová.
• Marináda a omáčka jsou hotové.

A useful point: hotové is also the form used for some other plural patterns, so the ending -é does not mean neuter here. In this sentence, it is agreeing with a plural feminine subject.

They are in the nominative case.

That is because they are the subject of the sentence: they are the things that are ready.

You can see the basic dictionary forms here:

• marináda
• omáčka

No case change is needed, because this is a simple X and Y are Z sentence.

Because grilovací belongs to a type of Czech adjective that often has -í in the nominative singular for multiple genders.

Here it modifies omáčka, which is feminine singular:

• grilovací omáčka = barbecue/grilling sauce

So although many adjectives change more visibly, this one already has the correct form as grilovací.

Compare:

• dobrá omáčka = a good sauce
• grilovací omáčka = a grilling/barbecue sauce

The adjective grilovací does decline in Czech, but not in the same obvious way as adjectives like dobrý / dobrá / dobré.

It is an adjective.

The verb is only jsou (are).
The word hotové is the adjective meaning ready / done / finished, and it works as a predicate adjective after the verb to be.

So the structure is:

• Marináda a grilovací omáčka = subject
• jsou = verb
• hotové = predicate adjective

This is the same basic pattern as in English:

• The marinade and the sauce are ready.

Yes. Czech word order is more flexible than English word order.

The neutral order here is:

• Marináda a grilovací omáčka jsou hotové.

But you could also say, for example:

• Hotové jsou marináda a grilovací omáčka.

That sounds more like Ready are the marinade and the barbecue sauce, which is not natural in English but is possible in Czech for emphasis or style.

So the original sentence is the most straightforward, but not the only possible order.

Because Czech does not have articles like English a / an / the.

So:

• marináda can mean a marinade or the marinade
• omáčka can mean a sauce or the sauce

Which one is meant depends on context.

In this sentence, English would probably use the if the speaker means specific items already being talked about, but Czech simply does not mark that with an article.

Yes. In this sentence, a is the normal coordinating conjunction meaning and.

It joins the two nouns:

• marináda
• grilovací omáčka

So the sentence is talking about both items together.

Be careful not to confuse Czech a with English a.
Czech a = and, not the English indefinite article.

You would make both the verb and the adjective singular.

For example:

• Marináda je hotová. = The marinade is ready.
• Grilovací omáčka je hotová. = The barbecue sauce is ready.

With two items:

• Marináda a grilovací omáčka jsou hotové.

So the changes are:

• je for singular, jsou for plural
• hotová for one feminine noun, hotové for two feminine nouns together

In standard Czech, no. That would be ungrammatical because the subject is plural.

Since there are two things, standard agreement requires:

• jsou hotové

not

• je hotová

So the correct sentence is:

• Marináda a grilovací omáčka jsou hotové.

Grilovací modifies omáčka and describes what kind of sauce it is.

So:

• omáčka = sauce
• grilovací omáčka = grilling sauce / barbecue sauce

This is just like English noun phrases such as:

• tomato soup
• barbecue sauce

In Czech, the descriptive word is usually an adjective, so grilovací agrees with omáčka.

Yes. Hotový / hotová / hotové is very natural for food when something is ready, done, or finished cooking/preparing.

So this sentence sounds normal in a cooking context:

• Marináda a grilovací omáčka jsou hotové.

It means the marinade and the sauce are prepared and ready to use.