Quamvis praedium parvum sit, magni pretii est familiae, quia ibi et labor et quies inter se conveniunt.

Because quamvis meaning although normally introduces a concessive clause, and in Classical Latin that clause usually takes the subjunctive.

So sit is the present subjunctive of esse, not the indicative est.
The idea is: Although the estate is small...

This is a standard grammar pattern, not necessarily a sign that the statement is doubtful or unreal.

Praedium is nominative singular neuter, and parvum is also nominative singular neuter.

They match because parvum is an adjective describing praedium. Together they form the subject phrase of sit:

praedium parvum = a small estate / a small property

Since praedium is neuter singular, the adjective must also be neuter singular.

The subject is still praedium, even though Latin does not repeat it.

A native English speaker may expect something like id magni pretii est familiae or a repeated praedium, but Latin often leaves out a subject when it is already obvious from the context.

So the structure is essentially:

Quamvis praedium parvum sit, [praedium] magni pretii est familiae.

This is a common Latin way to express value. Latin often uses the genitive of value with esse.

• pretii = genitive singular of pretium
• magni = genitive singular of magnus, modifying pretii

Literally, magni pretii est means it is of great value or it is worth a great deal.

So this is not the same as simply saying great price as a direct object; it is an idiomatic predicate expression with esse.

Here familiae is dative singular, meaning to the family.

With expressions of value like magni pretii est, Latin often uses the dative for the person affected or concerned. So:

magni pretii est familiae = it is of great value to the family

This is a good place to notice that familiae could also be genitive in form, but here the syntax clearly shows it is dative.

Quia introduces a causal clause, so it means because.

The sentence first gives a concession:

Although the estate is small...

Then it gives the main statement:

...it is of great value to the family...

Then quia explains why:

...because there work and rest harmonize with each other.

Each noun by itself is singular:

• labor = singular
• quies = singular

But together they form a compound subject: et labor et quies = both work and rest.

Because the subject is now plural in sense, the verb is plural too:

conveniunt = they fit together / they harmonize

Et ... et ... is a correlative construction meaning both ... and ...

So:

et labor et quies = both work and rest

Latin could have said simply labor et quies, but et ... et gives a more balanced and emphatic pairing. It highlights the idea that both elements belong together.

Inter se literally means among themselves or with one another.

Here it refers to labor and quies. So the idea is that work and rest are in harmony with each other.

It adds a sense of mutual relationship. Without inter se, conveniunt could still make sense, but inter se makes the reciprocal idea more explicit.

Convenire has several possible meanings in Latin, including:

• to come together
• to agree
• to be suitable
• to fit together

In this sentence, the best sense is something like go well together, fit together, or harmonize.

So labor et quies inter se conveniunt means that work and rest are well matched there.

It may feel unusual to an English speaker, but it is very normal for Latin.

Latin word order is flexible, and writers often arrange words for emphasis. In this sentence:

• Quamvis praedium parvum sit sets up the concession first
• magni pretii est puts the idea of value in a prominent position
• familiae comes after that to show who benefits
• ibi appears early in its clause to emphasize there
• et labor et quies gives a balanced pair before the verb conveniunt

So the order is not random; it helps shape the emphasis and flow of the sentence.