The plural of policemen does not fit with the use of "is singing"

I guess it's because nehany already indicates, that it's plural, so you already know that it's plural and therefore you don't need to put the following noun in plural.

How do we know that this is plural? I had "Some policeman is singing". The solution given was "Some policemen is singing." The solution lacks agreement of subject with the verb.

"Néhány" is translated as "some" or "a few", but the only accepted solution uses the word "some". Is that a mistake, or is there a grammatical reason why "a few" is not accepted?

Why not rendőrök?

Some of these sentences don't seem very practical. Why can we learn Hungarian in a context that is applicable to real world situations?

"I do not drive at home / otthon nem vezetek" is another example. They are everywhere in this course.

Apparently the word "cops" is not accepted:)

Should it not be sometimes policemen sing. Some policemen is singing either means valamilyen rendor enekel. Or it is simply improper English. We do not use some policemen is singing to represent plural policemen.

And the boys of the NYPD Choir are singing Galway Bay...

I dont yet what makes the sentence "Some police officers ARE singing" instead of "Some police officers sing."