The best way is to just sit down with them. They will surprise you.
I was 21 when I got pregnant and my bf was 20. Unfortuantly both my mom and his found out the wrong way. His mom saw us in the hospital and my mom got a call saying test were in from the doctor ( i ended up losing the baby). I wish i could have told them proberly. Mine were amazing with me and him they offered to help with everything and gave us so much advice.
Your parents love you. BOTH of you sit down with them, show them you are both adults and talk to them. tell them what you have planned and what you are going to do. make sure you sorta have an idea of what you are going to say to them. If they see you are being adults, they should take it a lot better. Good luck with everything and if you need to talk to anyone i am here.