I didn't have this problem mostly because when my daughter would have been in a rear-facing seat, we lived in China and had to take taxis everywhere. Seatbelts were iffy if they even had them. Many taxi owners cut them out. My daughter rode in the front carrier. What can you do?
I don't remember brands, though I think I've always had a Graco (except for the car seat I took on bus trips in China and with me to Africa which was a Chinese brand and smaller, and even it didn't fit properly in the bus seats.) I currently drive a Saturn VUE and I would not be able to fit more than two of those in the back seat. I used to take my nephews around with me, and the older one had to sit on the seat. The younger one would be in a rear-facing, and my daughter in a front-facing. They didn't interfere with the front seats.
Now she is in a "booster" seat with the back. I think I could fit three of those across, but I'm not sure.
I think about this sometimes. I'm one of 8, but we didn't have all those laws and regulations then. What do people with more than 2 children do? We had an extended body van growing up, but I don't think even that would fit all those carseats.