My Sister's Children

You didn't expect it, didn't see it coming. It was so normal. You visited your older sister, your niece and nephew. Sitting by the dinner table you were drinking some tea and her children, your niece and nephew were playing in your nieces toy kitchen. You ask your sister why the father of her children isn't around. Then after a while your sister asks you to sign something. She said its important but doesn't want to specify it further. Will you sign it? Not knowing what it is? Then something happened that changed your life forever.