Drag the URLs to the desktop from the address bar in Chrome. Now under System Preferences>Users & Groups, find your account, click on the lock to unlock the pane by entering an admin password, then click on Login Items and click eat "+" box below the login item windows, then a Finder window will open, navigate to the desktop and add the webloc files from those three sites. Now close System Preferences and when you log in, or when the Mac reboots, those three websites will open in the default browser. You can set that to Chrome in System Preferences>General. Now, getting those three sites to three different monitors is a bit more of a challenge. as Ashwin suggested.
Now, if this three monitor setup is really critical, get a huge Uninterruptible Power Supply and plug all of these devices into that UPS so that no power outage can force a reboot. (Don't forget the internet connection and all the routers/network devices you use to get to those three websites. And if the power draw is too large to guarantee against a long power outage, get an automatic generator that will supply power indefinitely. My house is protected by a natural gas fed generator that comes on after 10 seconds of no external power and my critical computers are all on UPS devices to cover that 10 seconds. So it's up to you how much you want to spend in time and money to guarantee those three websites are constantly being displayed.