Not if you're patient. They said they'll be moving around from the three different regions so you should be able to catch them over time. What I'm wondering is whether they'll be raid monsters or just wanderers. My bet is that they'll be the former.
Yes you need to travel to Antarctica to capture Entei, then you must travel to Germany to capture Raikou and after that you go to Saudi Arabia to capture Suicune. You can also cheat the system by placing your phone in the freezer on top of the frozen seafood to get Entei. Then you must dunk your phone in some beer to get Raikou. Finally you must allow a goat to eat your phone and wait a couple hours.