Avunculus dicit nepotem et neptem tam prudentes esse quam parentes eorum.

Because after dicit Latin is using an indirect statement. In this construction, Latin normally uses:

verb of saying/thinking + accusative subject + infinitive

So nepotem et neptem ... esse literally means the nephew and niece to be .... They are the logical subjects of esse, but in Latin they appear in the accusative.

Latin usually does not need a separate word for that in this kind of sentence. English says:

The uncle says that...

But Latin says:

Avunculus dicit + accusative + infinitive

So the idea of that is built into the construction itself.

Esse is the infinitive of sum, meaning to be. It is needed because the indirect statement is built around an infinitive.

It also links nepotem et neptem with prudentes:

nepotem et neptem prudentes esse = that the nephew and niece are wise

Without esse, the sentence would be incomplete.

Because prudentes describes two people: nepotem et neptem. So the adjective must be plural.

It is also a predicate adjective, so it agrees with the accusative subjects of the infinitive clause. The form prudentes works for masculine and feminine accusative plural, so it can describe the pair together.

This is the standard Latin pattern for an equal comparison:

tam ... quam = as ... as

So:

tam prudentes ... quam parentes eorum

means:

as wise ... as their parents

It does not mean wiser than or less wise than; it means the two are being presented as equal in wisdom.

In form, parentes could be either nominative plural or accusative plural, because those two forms look the same for this noun.

Here it is best understood as part of an implied clause, something like:

quam parentes eorum sunt

= as their parents are

So in sense it functions like a nominative subject in the understood comparison, even though the form itself does not show the difference.

Eorum is the genitive plural of is, ea, id. Here it means of them or, more naturally in English, their.

So:

parentes eorum = their parents
literally: the parents of them

Latin often uses this genitive form where English would use a possessive word like their.

A learner may expect suus, because suus often means his/her/their own. But eorum is a normal way to say their, and it can make the reference clearer.

A simple way to think about it is:

• suus = reflexive possessive
• eorum = non-reflexive their / of them

Here eorum straightforwardly points to the nephew and niece as the ones whose parents are meant. Latin writers often choose eorum when they want to avoid any possible ambiguity.

Yes. Both words can have either meaning, depending on context.

In this sentence, because the speaker is an avunculus—an uncle—the most natural meaning is nephew and niece.

Strictly speaking, avunculus means mother's brother, so a maternal uncle.

Latin can be more specific about family relationships than English. For example:

• avunculus = mother's brother
• patruus = father's brother

In many beginner translations, though, avunculus is simply translated as uncle.