Looking for a teen fantasy book

I read this book a few years ago so some details might be incorrect. Basically, there were these boys who were taken from orphanages because the looked like a prince who went missing. I can't remember if the whole royal family were killed in the pirate attack, but supposedly the heir was. One of the boys tried to leave and was killed. The people who got the boys wanted to put them on the throne as a puppet ruler, with everyone believing they are the lost prince. One of the boys can do a very specific coin trick that the prince could do and it turns out he was the prince but that's about where the book ends. I can't remember any names but I think there were about 3 boys after 1 was killed at the start. 1 was sick I think.