We are planning to open new branch of our business in different state. Do I need to create a clone of every page of our existing site and change titles and key words using new city's name or I could mix names of both cities in the same page(s)? Thanks in advance for your help!
Don't clone the pages on another site or the second site won't rank in google. I'd add the second city name to your page title and see what effect it has. Most likely you'll be fine and the new city will rank as well as the first one.
You need to change at least some contents otherwise it will be duplicate contents and one of the page will not do well in SERP