I am confused too, although i am dutch, but i think that is because my english is not good enough. I translated "there is being played and sung a lot".
Anyways, just keep in mind that when the dutch sentence contains 'worden' that means that something is still going on. If we use 'zijn' that means that something has happened and has ended already.
in one previous excercise (er wordt overal gezocht) er wordt was translated as "they are searching everywhere" (although a lot of people complained on the "they are" part). So I took note to always translate the "er wordt" as they are, when in passive voice exercises. However this one didn't accept my "they are singing and playing a lot". Unconsistent translation?
Again, it's a matter of context. In your example it's possible to translate it as they are. Sure it would be possible to stop accepting it there but then people will say but it is possible to translate it as that.
Accept it everywhere? No, because in other sentences it is not appropriate to translate it as they are.
how about in this context? Is "they are singing and playing a lot" an incorrect translation for "er wordt veel gezongen en gespeeld". If so, why? And why would "they are searching everywhere" be a good translation for "er wordt overal gezocht" vs "there is searching everywhere"?