Gener cum nuru nondum venit, sed mater dicit eos mox adfuturos esse.

Because the grammatical subject is only gener (the son-in-law). The phrase cum nuru means with the daughter-in-law and is just a prepositional phrase, not a second subject.

So Latin is saying:

• gener ... venit = the son-in-law ... has not yet come
• cum nuru = with the daughter-in-law

If Latin wanted both of them to be the subject, it would say something like gener et nurus nondum venerunt.

Because cum takes the ablative case, and nuru is the ablative singular form of nurus (daughter-in-law).

So:

• dictionary form: nurus
• ablative singular: nuru
• cum nuru = with the daughter-in-law

This is a good form to notice, because nurus is a fourth-declension noun, and its ablative singular ends in -u.

Because in Latin, venit can represent either:

• present: he comes
• perfect: he came / he has come

In texts without macrons, those two forms look the same. Here the context makes the meaning clear:

• nondum venit = has not yet come

That fits naturally with the next part, where the mother says they will be here soon.

If macrons were written, the perfect would be vēnit.

Because eos refers to gener and nurus together as a group, and in Latin a mixed group normally takes the masculine plural.

So even though one person is female, Latin uses:

• eos = them (masculine plural, used for a mixed group)

It would be eas only if the whole group were feminine.

Because Latin usually does not use a that-clause after verbs of saying, thinking, knowing, and so on. Instead, it uses indirect statement.

English says:

• Mother says that they will be here soon

Latin says:

• mater dicit eos mox adfuturos esse

So instead of a separate word for that, Latin changes the structure of the clause.

This is the accusative-and-infinitive construction, often called indirect statement.

Its basic pattern is:

• verb of saying/thinking/knowing
• accusative subject
• infinitive verb

Here:

• dicit = says
• eos = the subject of the reported statement, put in the accusative
• adfuturos esse = the infinitive part, meaning will be present / will be here

So literally it is something like:

• Mother says them to be going to be here soon

But in normal English we translate it as:

• Mother says that they will be here soon

Because in an indirect statement, the subject of the reported clause goes into the accusative.

So although they would be nominative in a direct statement, Latin changes it to eos after dicit.

Compare:

• direct idea: ei mox aderunt = they will be here soon
• indirect statement: mater dicit eos mox adfuturos esse

This is one of the most important Latin sentence patterns to learn.

Adfuturos esse is the future active infinitive of adsum, adesse, which means to be present, to be here, or sometimes to arrive/be on hand depending on context.

It is formed from:

• the future participle adfuturus = about to be present / going to be here
• plus esse

Because it agrees with eos, it appears as:

• adfuturos = accusative masculine plural
• esse = infinitive to be

So eos mox adfuturos esse means:

• that they will be here soon

Because Latin has no articles. It does not have separate words for the, a, or an.

So:

• gener can mean the son-in-law or a son-in-law
• mater can mean the mother or a mother

The context tells you which English article makes sense.

The word order is meaningful, but Latin is much more flexible than English.

This sentence puts the main pieces in a natural order:

• Gener cum nuru nondum venit
• sed mater dicit eos mox adfuturos esse

The adverb mox (soon) is placed near adfuturos esse, which makes good sense. But Latin could move words around more freely than English without changing the basic grammar, because the cases and verb forms show how the sentence works.