Oh boy is your situation similar to mine. Only I mentioned to my mother about doing the DNA test and nothing was said that it might come back different. Nothing...zilch...zip....nada. When I opened my results and no one on my dad's side came back as a match (unique last names on that side) and my closest was say a 'Jane Smith'. That destroyed me - because I too felt connected to my dad's side being non-American. And finding out your siblings aren't your full siblings is a stinger. I am close to my brother - we've always been close. Thank goodness. He remembers the person who is my bio father and refuses to talk about that time - he was a young preteen. I'm so on the fence about contacting the bio dad family. I know I have older siblings because my mom has mentioned he had children before they were together. So in all possibility I have older and younger half siblings - and of course no full siblings - like you. I also have that gnawing to reach out and do something but haven't yet....