Also, just because your apartment has specific "quiet hours" does not mean you are free to make loud noises consistently outside the quiet hours. In my building, the lease specifically defined the quiet hours (10pm - 8am), but in a separate clause it also says something to the effect that you are not supposed to make noise that impact neighbors. It is more subjective, but your kid's playing piano most likely fits the bill.
Of course, if push comes to shove, you can threaten the couple that you are going to tell the management about their dog. You will probably win because old people love their dogs. Although I have to say, you may become a public enemy in the neighborhood for requesting to have an old couple evicted because of their only companion, say, a little chihuahua. Again, rules are rules (that's why I think you will win the battle!), but sometimes there is also common sense and empathy.