Here is a grammar explanation of this kind of usage of "het", "dat" and "dit" in Dutch to mean "they", "those" and "these": http://www.dutchgrammar.com/en/?n=Pronouns.Ps04
The site I linked mostly explains the use of "het". In cases like this, "het" would mean "they", "dat" would mean "those" and "dit" would mean "these".
Het zijn verloofde koppels. - They are engaged couples.
Dat zijn verloofde koppels. - Those are engaged couples.
Dit zijn verloofde koppels. - These are engaged couples.
Can "Het/Dat/Dit zijn verloofde koppels." be translated to German with "Es/das/dies sind verlobte Paare."? You can't really translate that sentence to English, though, because the closest thing in English would be "they/those/these are".
What about sentences like this one, then? It has to be clear what you're referring to and the people were probably mentioned before.
"(…) Diese sind verlobte Paare, aber jene/die (da) sind verlobte Paare."