Welcome to planDisney, Clare! I'm so glad that I get to answer your question today.
Bibbidi Bobbidi Boutique is a coveted experience for many families at
Disney World, so I understand you're feeling a little anxious about getting two simultaneous appointments for your girls. I certainly don't think this is an impossible feat, but it will be challenging, as you've experienced. It's such a popular booking that getting one is worth celebrating, getting two at the same time would be incredibly lucky. My best advice is to keep trying! Check back on the availability of reservations as frequently as you're willing to. Guests are changing their plans all the time, so you never know what kind of magic might happen.
I see that you also asked about same-day appointments, and this is also a possibility! I was at
Magic Kingdom this weekend, and I saw that the Boutique had a sign out front letting guests know that same-day appointments were available. Even if you don't see this sign, it never hurts to ask. I also recommend that you remain open-minded to changing the date of your reservation or booking reservations that aren't simultaneous. This will give you a bit more freedom to find two timeslots!
Best of luck, Clare, and have a magical day.
Jessica