This is a small thing, but "on the street" sounds strange to me (though not necessarily wrong). I would almost always use "in the street" for people or things literally in the roadway (which I assume the Chinese means). I would "on the street" to refer in a slightly figurative way to homeless people, back alley drug dealers, etc.

There are a few people on the street. This should be accepted

Marked the word aren't incorrect for are not!

The sentence sounds to me like 'in the streets' should be accepted as well.

The Chinese sentence sounds a little awkward to me (native speaker). A more natural way to put it is 街上人不是很多 (or simply 街上人不多).