Question

Currently watching on netflix and I had to pause because I'm so confused??? I only found out in the confrontation part that Belle is Piolo's daughter??? Huh?? Why does Belle call Joshua and JK "kuya"? I guess it's fine that she calls Maricel "Mama". I think there's a part at the beginning where Belle is said to be the youngest?? Im so confused. So she's Joshua and JK's niece all this time??? Then how did she become Piolo's daughter? I thought she was in the US this time?? Did she have time to go home??