Just sit your family down, and tell them. As hard as it is, as much as you'll stutter they need to know. Your family love you and sure they might be mad at first but not because they don't want the baby, but because they are worried how you'll cope and how you feel deep down.
I sat with my mum and told her first and we rang the family members together and she told my dad for me, they were great when I thought they'd flip but honesty is always the best policy. My mum bought me an extra two tests and we sat by the fire just after christmas and when my dad came home from work, first thing he said was "where we gunna get you some expandables" lol.
Your parents could react anyway, you won't know if you don't tell them.