"I am bilingual, but my parents are not."
Translation:Jeg er tosproget, men mine forældre er ikke.
Is the second 'er'' really compulsory, as in English? In many other languages, it is isn't.
Yes, unless you switch the words around, but that would also change the meaning of the second sentence. 'men ikke mine forældre' in context could be understood correctly, but would in reality state that you are not your parents. Native speaker here :)
Would something along these lines in Danish be possible? "..., men mine forældre er det ikke" or "... er ikke det"?
First one, yes, but not the second one. Second one doesn't make sense in Danish at all, not even when posing as a question. Native speaker here :)