"Those who are young are standing on the bus."
Translation:Azok állnak a buszon, akik fiatalok.
It's.. possible but sounds a bit confusing, much like the English equivalent would sound: "Those stand on the bus who are young." Grammatically valid, but misleading.
It's better to keep azok in focus here, like the given translation does, so you know that you have to connect azok to akik in the relative clause. But there are other ways you can say this:
- Azok, akik fiatalok, a buszon állnak. Here you don't need to place focus on azok because the relative clause follows immediately.
- A buszon azok állnak, akik fiatalok. The bus is the topic here, it's not much different from the original sentence, but you also can shift the focus here by saying...
- A buszon állnak azok, akik fiatalok. Here you have azok and relative clause directly connected again, but with the kind of focus that you attempted in your sentence.
- Akik fiatalok, azok állnak a buszon. It's also possible to place the relative clause first, which you usually wouldn't do in English.
You have the clauses backwards. There are two clauses in this sentence: the main clause, "Those are standing on the bus"/"Azok állnak a buszon", and the dependent clause, "who are young"/"akik fiatalok".
"Akik fiatalok" can be inserted practically anywhere in the main clause, but it has to stick together. You put fiatalok in the main clause and "a buszon állnak" in the relative clause, so that doesn't match the English sentence.