Earlier quoted context omitted.
You might want to double-check that. I was looking at a thread specifically about 3 carseats in the back of a Model 3. There are several options. You might need new carseats. But I managed to get our 3 kids in the back of my first generation Nissan Leaf, which I think is slightly smaller.
The 1st generation Leaf was larger inside. I like the Leaf's interior much more than the Model 3. (But, overall the Model 3 is a much, much better car.)
The first gen leaf is higher, for sure, because it's almost a crossover like the Model Y (and this is nice for loading and unloading the kids, altho it hits the efficiency slightly), but I'm really not sure it's any wider. You really can fit 3 kids abreast in a Model 3.