Pregnant at 17

Me and my fiancé (engaged before we found out) have been together almost 4 years. I'm going to be a senior and I'm on the path to being a neonatal nurse practitioner after I graduate this may. I've always been a good kid and my dad and step mom know I used to be sexually active with him but don't think I am now or at least they pretend I'm not. Me and my fiancé have a great relationship and we're actually happy about this...after I finished crying my eyes out haha...my biggest concern is telling my dad and step mom. They see getting pregnant before 35 as throwing your life away and my step mom has always said I would end up making a mistake (we dont really get along). I know my parents are going to b angry and I've talked with his parents and them having had his sister in the same fashion are supportive and say that I can move in with them if need be. The thing is I'm afraid my dad will want to disown me or something, I already know my step mom will never want me around my sisters again for fear of influence. I just want to get an idea of how the conversation might go. I feel a lot of guilt and shame not so much for what I did but for being kind of happy about it. I've always thought that having a family is the ultimate goal...not money and wealth like my parents. If you could just tell me how your conversation happened so I could get an idea that would be extremely helpful. (Oh and my parents don't know about our engagement and my dad is kind of betting on the fact that we will break up when I graduate this may..they don't believe in high school sweethearts AT ALL.)