There is not a lot wrong with "factor" there, but it sounds circumlocutory. Your second idea is better: "The chance of rollover for a 12-passenger car is far greater than for an 8-passenger car."
Here's the thing. I answer one simple question, and then you load me up with a pile of work that if my boss did it, I'd ask for a raise. Please start a new thread instead. (I made a rhyme that time.)