Exactly. Book twice for 4. You’ll need two separate MDE accounts to accomplish this. I log in under my account on one device, and my sister’s account on another device. Then when you check in at the podium, ask to be seated at one table. I’ve had like a 95% success rate of being seated together. We show up a few minutes early because sometimes it means a little extra wait.
Since our last 10-person trip last year they’ve added the ability to modify party size online when you do online check-in at the restaurant. I’m not sure if it would let you go so far as to double a party size, or if you’d run a risk of one party getting hit with the no-show fee even though they’re there. Maybe someone with more recent experience can weigh in on that, but I would be inclined to skip online check-in when trying to merge tables for that reason. Good luck!