"Who are in the parliament?"
Translation:Wie zitten er in het parlement?
The parliament is considered, in the Netherlands, both the first and second chamber ("eerste en tweede kamer"). I'm not sure how it works in other countries but I'm quite sure the UK has quite the same structure with the lower and upper house if I remember correctly. Both of the chambers (and houses) consist of parties who are chosen by the people, democracy.
So you can interpret it as what is considered the parliament (which would be for the Netherlands first and second chamber) or which parties are a part of the parliament. I personally think the first one is more likely.
OK, if it is not asking who is physically in the parliament right now then 'who makes up the parliament' sounds better to me.
The UK is also bicameral, we have a house of lords, not democratically elected but partly politically aligned, and a house of commons, democratically elected, which are part of what we would call and understand as Parliament. The corresponding entity in the US is Congress (dutch Congres I guess) so parliament might have a more general meaning there.