Ouvir is also listen right? So what's the difference between ouvir and escutar?
You made me look for them in the "pai dos burros" :-D (literally "father of the dumbs", an expression sometimes we use for the dictionary...) So, that's what I found: formally "escutar" means precisely "to listen" (the action or effort to hear), but I can say with my experience that it is widely used in the sense of "to hear". In the other side, "ouvir" means both "to hear" and "to listen" even in my dictionary (Dicionário Houaiss da Língua Portuguesa, a very authoritative one). Conclusion: if you want to be completely formal, "escutar" should be translated only into "to listen". But in real life language, "ouvir" and "escutar" are interchangeable and mean both "to hear" and "to listen".
"They can't" means that they lack the ability (or the permission) to do something. "They don't" means that they choose not to do something.
In my humble opinion, the sentence in Portuguese means both. I believe DL should accept "Can't they listen?" as well as "Don't they listen?". Actually, I think DL should also accept "to hear"...