Learn Danish: Deres kærlighed til hinanden er stærk. - Their love for each other is strong.

Prepositions rarely translate one-to-one between languages. In Danish, the fixed expression for directing feelings toward someone is often made with til. So 'love for' becomes kærlighed til.

Is hinanden always placed directly after the preposition like this?

Yes! Just like in English, when hinanden (each other) is the object of a preposition, the preposition comes right before it. Here, it acts as the object of til.

Could we rephrase this using the possessive form hinandens?

You could say Hinandens kærlighed er stærk (Each other's love is strong), but it changes the focus slightly. Using the prepositional phrase til hinanden emphasizes the direction of the love flowing between the two people.

Why doesn't the adjective stærk have a -t or -e ending here?

Stærk describes the noun kærlighed, which is a singular common gender (en) word. Because it is singular and common gender, the adjective stays in its base form without any added endings.