Capsarius et unctor in balneo laborant.

Because capsarius et unctor is a compound subject: the capsarius and the unctor. In English, we also use a plural verb with A and B: The attendant and the masseur work.

So:

• capsarius = one person
• unctor = one person
• capsarius et unctor = two people together

That is why the verb is laborant = they work.

They are both nominative singular, because they are the subject of the sentence.

Even though they do not look the same, they are still both nominative:

• capsarius — nominative singular
• unctor — nominative singular

Latin nouns can belong to different declensions, so subjects do not all have the same ending.

Because in takes the ablative when it means in or inside in the sense of location.

Here the sentence describes where they work, not motion toward somewhere:

• in balneo = in the bathhouse / in the bath

By contrast, if there were motion into something, Latin often uses in + accusative:

• in balneum = into the bathhouse

So:

• in + ablative = location
• in + accusative = motion into

Balneo is ablative singular.

It is ablative because it follows in in a location phrase:

• in balneo = in the bathhouse

The basic dictionary form would be balneum, and balneo is one of its declined forms.

Et means and. It joins capsarius and unctor into one compound subject:

• capsarius et unctor = the capsarius and the unctor

It is a very common Latin conjunction.

Latin does not have articles like English the and a/an.

So a noun like capsarius can mean, depending on context:

• a capsarius
• the capsarius

The same is true for the other nouns in the sentence. Latin leaves this to context.

Laborant is:

• present tense
• active voice
• third person plural

It comes from laborare = to work.

So laborant means they work or they are working, depending on context.

Because Latin verbs usually include the subject information in the ending.

In laborant, the ending -ant tells you the verb is third person plural, so they is already built in.

That means Latin often does not need an explicit subject pronoun such as ei or illi.

Yes. Latin word order is more flexible than English word order because the endings show the grammatical roles.

So this sentence could appear in other orders, for example:

• In balneo capsarius et unctor laborant.
• Capsarius in balneo et unctor laborant.
• Laborant capsarius et unctor in balneo.

The basic meaning stays the same, though different orders can slightly change emphasis.

No. They are both masculine nouns, but they belong to different declension patterns.

• capsarius is a second-declension noun
• unctor is a third-declension noun

That is one reason their nominative singular forms look different. Latin subjects do not all have to end alike.

It can depend on context and how the translator chooses to phrase it.

Literally, in balneo means in the bath / in the bathhouse. But in natural English, a translator might sometimes say:

• in the bathhouse
• at the baths
• in the baths

The Latin grammar is still the same: it is a location phrase with in + ablative.

You can divide the sentence like this:

• Subject: Capsarius et unctor
• Place phrase: in balneo
• Verb: laborant

So the structure is:

[The capsarius and the unctor] [in the bathhouse] [work].

Either can be correct.

The Latin present tense often covers both:

• they work
• they are working

English chooses between these more sharply than Latin does. The context usually tells you which sounds better.