Pregnancy announcement for grandparents!! Help!

We don’t plan on telling my mom and in-laws we’re expecting until after our February 11th appointment. Telling them same day. Thing is my MIL will be at our place watching our 2 kids. She obviously knows we have an appointment but doesn’t know for what. Well my mom lives about 50 minutes away, MIL is about that far too. She’s coming the night before. My mom is on the way home from our appointment but we won’t have our kids with and I want them part of the announcement. Racking my brain trying to figure this out haha I want it special and creative as this will probably be our last baby. If it’s twins then it’s a whole nother ball game. My mom isn’t very observant but my MIL is. Help me plan an announcement 😁