Heillä on hyvä suhde.

Literally, heillä means something like at them, with them, or in their possession.

In this sentence, it is how Finnish expresses they have. So:

• heillä on = they have
• literal structure = at them is

This is a very common Finnish pattern.

Heillä is the adessive form of he.

• he = they
• adessive ending = -lla / -llä
• he + illä gives heillä

With pronouns, these forms are learned as whole forms:

• minulla = I have
• sinulla = you have
• hänellä = he/she has
• meillä = we have
• teillä = you plural / you formal have
• heillä = they have

The adessive often has meanings like on, at, or with, depending on context.

Because Finnish normally does not use a separate verb like English to have.

Instead, possession is usually expressed with this pattern:

possessor + olla

So:

• Minulla on kirja = I have a book
• literally: At me is a book

And here:

• Heillä on hyvä suhde = They have a good relationship
• literally: At them is a good relationship

So this is not a special exception — it is the normal Finnish way to say that someone has something.

Because heillä is not the grammatical subject here.

In this kind of possession sentence:

• heillä = possessor, in the adessive case
• on = form of olla
• hyvä suhde = the thing that exists / is possessed

Finnish does not make the verb agree with heillä the way English agrees with they.

So even though the meaning is they have, the structure is really closer to:

• At them is a good relationship

That is why on is correct.

Because hyvä suhde is not an object here.

English learners often expect something like an object after have, but Finnish is not using a real have-verb here. It is using the possession structure with olla.

So:

• Heillä on hyvä suhde uses hyvä suhde in the nominative
• it is not treated like a normal direct object

Also:

• hyvä agrees with suhde
• both are singular nominative

If you used hyvää suhdetta, that would suggest a different structure and would not fit this sentence naturally.

Because adjectives in Finnish usually agree with the noun they describe in case and number.

Here the noun is:

• suhde = singular nominative

So the adjective must match it:

• hyvä suhde

If the noun changed, the adjective would change too:

• hyvässä suhteessa = in a good relationship / in a good relation
• hyvät suhteet = good relations
• hyviä suhteita = good relations, in the partitive plural

So hyvä is in this form simply because it matches suhde.

Because Finnish has no articles.

There is no direct equivalent of English a/an or the in normal Finnish grammar.

So:

• hyvä suhde can mean a good relationship
• in another context, it could also mean the good relationship, depending on what is already known

You understand which one is meant from context, not from an article.

Yes. That is also correct, but the focus is a little different.

• Heillä on hyvä suhde = They have a good relationship
• Heidän suhteensa on hyvä = Their relationship is good

The first sentence uses the common Finnish possession pattern.

The second sentence talks more directly about their relationship as the topic.

So the difference is mostly about focus and style, not basic meaning.

No.

Suhde is a general word meaning relationship, relation, or connection.

Depending on context, it can mean:

• a romantic relationship
• the relationship between two people
• relations between groups or countries
• an abstract relation between things

So Heillä on hyvä suhde could mean:

• they get along well
• they have a good personal relationship
• they have a good romantic relationship

Context tells you which one is intended.

Yes, but Heillä on hyvä suhde is the most neutral word order.

Finnish word order is more flexible than English, and changing it usually changes the emphasis, not the basic meaning.

For example, other orders can sound more contrastive or literary. But for a normal, neutral statement, Heillä on hyvä suhde is the best choice.

So if you are learning the sentence pattern, this is the form to remember first.

Yes, this is perfectly normal and correct Finnish.

It sounds standard and natural in both writing and careful speech.

In more casual spoken Finnish, people may sometimes use more colloquial pronoun choices, but Heillä on hyvä suhde is an excellent standard model sentence to learn.