Learn Polish: Słychać dzwonek, bo państwo Kowalscy chcą nas poznać. - I can hear the doorbell, because the Kowalskis want to meet us.

In Polish, surnames ending in -ski or -cki act like adjectives. To talk about a couple or a family (a mixed-gender group), we use the masculine personal plural form, which changes -ski to -scy.

What exactly does państwo add to Kowalscy?

Państwo is a polite title for a married couple or a family, roughly equivalent to "Mr. and Mrs." or "The... family". While you could just say Kowalscy chcą..., adding państwo is the standard, polite way to talk about them in Polish.

Why doesn't the sentence say słyszę (I hear) instead of słychać?

Słychać is an impersonal verb that means "can be heard." Polish often uses impersonal verbs like this to describe things happening in the environment, focusing on the sound itself (the doorbell ringing) rather than the specific person listening.

Is dzwonek the subject of the first part of the sentence?

No, it is actually the direct object! Impersonal verbs like słychać take the accusative case. Because dzwonek (doorbell) is an inanimate masculine noun, its accusative form looks exactly the same as its nominative (subject) form.