If you want to literally say "Eastern Europe," you would have to say «a Europa oriental». In this sentence, you «o leste europeu», which is the more common way of expressing these ideas. «europeu» is the adjective "European," and «leste» is the noun "East." Therefore, it literally translates in English to "Her family is from the European East."
west = oeste / east = leste (first E has an open sound). but if you say thay with a closed sound (like /lêste/) it becomes the verb read conjugated in the simple past for the 2nd singular person. "tu leste a mensagem que te enviei?" = did you read the message that i('ve) sent you?". LEU (conjugated for ele, ela, você) is more common than LESTE.
Is this yet another Brazilianism that we are supposed to just know? All of my resources say that 'é do' means "from", 'leste' is "east" and 'europeu' is "European". So this sentence would say 'is from east European' which makes NO SENSE. The family is either of 'east european descent' or 'from eastern Europe' but this sentence says neither. Isn't Europe given to us, even by Duo, as 'europa' and not 'europeu'?
Her family are from eastern Europe is perfectly valid in British English where the plurality is left for the writer to determine. Are they all from eastern Europe? Her family are from eastern Europe (= the common sense reason why British English leaves this open to interpretation).
Yes, so my contention is the British way is more useful - it allows more 'colour'. In the same way you say 'the couple are having separate holidays this year'. Family is a collective noun, it's the sum of its parts. To illustrate this by extension (and I have heard this in the USA).
The family is Republican. US Oh, it is, is it? The family is a Republican Family. (British, for clarity using 'is' to emphasise the solidarity and consistency). Oh, it is, is it?
Extending: The family is Republicans and Democrats. US - starting to decay. Oh, they is, is they? - going, going, gone.
The family are Republicans and Democrats. Oh, they are, are they? British, consistent.
Why can't you say "it is, is it?" in the second situation as well. I think the sentence would sound better with "is composed of" instead of simply "is." Either way, Duolingo prefers to use American English by default for some reason.
Also, the second situation, sentences where the verb is "to be" and what comes before is grammatically singular while what comes after is grammatically plural, is something with which all languages struggle. Interestingly, all of the Romance languages deal with this by conjugating with whatever comes before: «A família é...», «La familia es...», «La famiglia è...», « La famille est... ».