You'll need to configure your router for port forwarding if you're attempting to access your macs from the internet.
An easier solution is to use Logmein which is free for personal use. You'll need to worry about port forwarding anything with logmein.
I agree with Maflynn....but if you want to do it
First off you will need a static IP address from your ISP, if you are at home then you probably have a dynamic address and will have to use DYNDNS and set it up on one of your Macs.
You don't have to install ARD on all four machines...only the machine you are using remotely to remote into the other machines.
After you have your static IP or dyndns then you will need to set your macs to have a internal static IP (192.168.x.x or whatever your subnet is)
After this configure port forwarding on your router. And since you want to remote into more than one on the same internal network you must use public and private ports. So the public ports would be 3283, 5900 and the private ports would be XXXX, XXXX and point it to one of your internal macs. The private port numbers would have to be different of course for each mac
Then after this go to your Macs and then click on Sys Pref. and then sharing and turn on Remote Management - selecting all the options.
Then make sure that awake for network access is turned on under Network in sys pref too.
Then when you are away from home open up ARD and connect using your static IP address or the DYNDNS address and the public port number you setup above for each machine.
For example here is how one of my clients look with fake DYNDNS address
sharemypc.dyndns.com:5901 - first mac
sharemypc.dyndns.com:5902 - second mac
sharemypc.dyndns.com:5903 - third mac
Did I mention that logmein is simpler and just an install away? This stuff above is pretty advanced and if not configured correctly would not work. ARD is meant more for internal use and for Sys Admins