Thanks NESunrise.  I just hate the idea of getting anyone in trouble and that really isn't my goal. I just want to get the issue taken care of. You are right. They will get over it and move on.  The city will just send them letters warning them to cut their branches or shrubbery or they will come do it and put the cost on their property bills. I really think that is the better way to go. 
 

Thanks Sam. I agree that the likelihood that it will not end well if I tried to talk to these people is too great. I am much more comfortable letting the city take care of it. They have the authority to and it is really their place not mine.

I would certainly not go to the door.  You don't know how these people will take the "intrusion."    I would just go directly to the city office that would handle this.  It's not big deal.  They'll get a letter.  It happened to me.  I live on a corner and didn't know that my tree branches were blocking the stop sign on the side street.  It's a dead end (or "no outlet" and they are now politically correctly called) so there was no reason for me to be on that street.  I took care of trimming the trees and that was the end of it.  Sidewalks should be safe.  There are probably rules about what a safe sidewalk is in your city.