Learn Russian: Жители любят свой жилой комплекс. - The residents love their residential complex.

свой is a reflexive possessive pronoun that refers back to the subject of the sentence (Жители). Since the residents love their own complex, you must use свой. If you used их, it would mean they love some other group's residential complex.

The words жители and жилой look related. What is the root here?

Both words share the root жи- related to living, which you know from the verb жить (to live). жители translates to residents or inhabitants. The adjective жилой specifically means residential and is strictly used for buildings, areas, or rooms meant for living in.

Is there a common real-world abbreviation for жилой комплекс?

Yes! In modern Russian, a residential complex is almost always referred to by the abbreviation ЖК (pronounced жэ-ка). You will frequently see this in real estate or hear it in daily life, such as Мы живём в новом ЖК (We live in a new residential complex).

How could we expand this sentence using the lesson's target grammar to say 'The residents love not only their apartment, but also their residential complex'?

You frame the two objects with the two halves of the conjunction. To say 'The residents love not only their apartment, but also their residential complex', you would say: Жители любят не только свою квартиру, но и свой жилой комплекс. Both objects remain in the accusative case.