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In terms of seatbelts, it's a total of five. Two bucket seats in the front, and a rear bench seat in the back. If the baby is in a car seat, you'd be hard pressed to fit three adults in the back, unless they're VERY friendly and are also unconcerned about seatbelts.
You could do 2 adults in front, another adult in the 2nd row with a baby in a car seat, and two more adults on the other side, one sitting in the lap of the other, but that will only work for nine months and then you'll need another car seat.
If you really wanted, you can fit 5 adult passengers, all with seat belts. Those 5 passengers can each carry at least 1 baby. That's 10 people (only possible with a Tesla due to autopilot for the driver, otherwise 9) You STILL have the option of a frunk, which obviously will hold one adult (reference LikeTesla) and I'm pretty sure another baby. This still leaves the rear trunk of the MX, which is unique in that you have essentially a footwell. You can easily fit 2 adults sitting upright and carrying 2 more babies and allowing them to stretch their legs. You will need to remove the rear well cover though. They will also fall backwards on braking since there is 3rd row seatback holding them up, so obviously you need 2 more adults to sit back to back with them. These two will not be able to hold babies as they do not have room for their legs and their knees will be in their chest.
All in all, it fits 18 people. 80% more than your original estimate.
Let us not also forget the MX is designed to tow, even with a 5 seater. You may be able to pull a Ford E-350 15 Passenger van, which will hold at least another 15 People and 15 babies.
***Disclaimer: All of this may affect your wh/mi. Crash testing, safety, and survival rates may vary based on your situation. No guarantees made on legality, feasibility, or truthfulness to any of these statements.