You’re not being realistic if you think we can’t beat car dependency, or we have to completely eliminate cars from society. We need to eliminate the system that ensures that cars are the only option, something everyone is forced to own because they make everything else far less safe and convenient. That is a choice that is repeatedly and consistently made in favor of car dominance over humans, and it shouldn’t be.
Your example is unambiguously plural. It’s not a good illustration of “they” creating confusion.
It’s truly not a problem. I could contrive a reason to talk about a couple (they plural) and a nonbinary person (they singular) and end up with sentences where you don’t know which I’m referring to, but the exact same issue happens if I’m telling a story about two “he” or “she” subjects. And it’s solved in the same way.