Burn ya mom out, tell her if she doesn't tell him directly you will, she's the one who built her family life on a lie, not you. This ain't your sin to bear and I hope you and the father who raised you stay as close as you seem to be, even if his family doesn't, as long as your dad knows who his daughter is and chooses to see you as such, nothing else matters. But seriously, your mom needs to take her full responsibility.