Dress tips please!! SOS

So my fiance and I are eloping at city hall next week... neither of us are big party people and don't want to make a huge deal about it. However, in 2 weeks we are having a cookout for just close family friends to celebrate. EXTREMELY CASUAL.

Oh, I'll also be 36 weeks pregnant 🤦‍♀️ his sister said she wanted to bring her camera so I have NO IDEA what to wear. Something cute and obviously maternity, but I want to be comfortable sitting around a fire and chasing after my nieces and nephews outside. I have zero idea what to wear... my whole wardrobe is stretchy lately 😂 send help!