It doesn't have a dot, so I deleted "This is a married couple", which is after all a sentence.
But it can both mean "a married couple" as well as the idea of "marriage".
Back to the "This is a married couple": in a sentence "This is Y", you can sometimes omit the verb. It's hard to say when it's okay and when it doesn't sound good. But theoretically, it could mean it, if only it had a dot at the end.
I respectfully disagree Panie Marku: the fact that the phrase given isn't explicitly punctuated as a full sentence doesn't mean that it can't translate to anything that could be a full sentence: indeed, the remaining accepted translation, 'this marri[age/ed couple]' could also be said as a full sentence (in some sense at least, i.e. one that would need a full stop at the end), for example if it was the answer to the question, "Which marri[age/ed couple]?" but of course that doesn't mean that 'to małżeństwo' without a full stop should not be able to be translated to that either, because as you said, 'this marri[age/ed couple]' doesn't have to be a sentence on its own but can also be just part of one; however, so can the one you deleted, the 'this is a marri[age/ed couple]' one, namely if it's a clause of a sentence that also has other clauses, for example, it would be required not to have a full stop after it if it was the beginning of the sentence, "This is the marri[age/ed couple] I was telling you about." ~ "To małżeństwo o którym ci powiedziałem" I believe (although actually would one normally always include the 'jest' in that sentence?).
Well, I guess that you are right, there's probably no harm in accepting it. Added back. Luckily Tree 2.0 will almost not have any such 'phrases' at all.
For your sentence, I believe the best way would be to interpret "the" as "this" and to say "To jest to małżeństwo..." (This is this married couple...).
Accepting "This is a marriage" is already a stretch (you don't have a dot at the end of the phrase here, so in fact it is rather a noun phrase "this marriage" and not a sentence). And "This is a wedding" is wrong.
"wedding" is either "ślub" (the ceremony) or "wesele" (the wedding reception).
"małżeństwo" is either the state of being married (Bob and Anne's marriage) or the married couple.
"małżeństwo" is either the state of being married, so the relationship indeed, or 'the married couple' (not necessarily newlyweds, simply two married people). The only problem I have is that this here is not a sentence, because it doesn't end with a dot. But ok, ADJD4 persuaded me to accept it. And if "This is a marriage" works, then "This is marriage" seems fine as well. Added.