Also driving in a seating position with your arms stretched out is incorrect.
I second the point that there is plenty of room back there if this isn’t primarily a people mover. If you’re taking the kids to soccer practice a couple times a week and then commuting the rest, no problem. I have three kids in the back a couple times a week and they are fine for short trips. That includes fitting in one booster seat for the smallest, who needs it by law. They wouldn’t enjoy being crammed in there for an hour a day, 5 days a week, though.