Generally speaking, putting "here" at the end of a sentence is absolutely fine. But in this sentence, it seems strange.
For simplicity, let's pretend the exercise sentence is a statement rather than a question. First, we want to indicate that "They are here," and then we want to qualify that by adding "without their families." Shifting "here" to the end inserts the qualifying phrase into the middle of the primary subject-verb part of the sentence in a weird way. I hope this makes sense.
We appreciate your asking the question. When it comes to questions about how English works, we are usually bombarded by comments along the lines of "It doesn't matter how English works, we are learning Czech here!!!" :-)