Unsure of how to tell family

My fiance and I (21&20) are currently ttc. Haven't conceived yet. But my mother and grandmother don't know. Whenever I bring up "I have news" their first response is "You aren't pregnant are you?!" When it does happen I'm just unsure of how to tell them. My older brother had a badly planned pregnancy and they were mad at first but got excited about it as it got closer. (Niece no longer in picture due to brother and ex having a falling out and being stupid) So I wonder if they'll be excited to have a great/grandchild that will stay in the picture. I suppose this is more of me just venting because it stresses me out a bit. Any ideas on how I can tell them when it does happen? Or am I overthinking it? Thanks in advance.

**Thank you for the responses!!