Depending on how how often you want to have your backups brought up to date, there are a few ways to do this...
1) You can, when you think of it, just copy the files over. The first time you do it will take hours, I would imagine, with 2TB if you are using USB to connect. And for each HD, it will take time. Considerably less time if you have FW or eSata. The next time you copy over it will ask if you want "replace" existing files. I believe the system is only checking file name and date, and not size. So if you choose to not "replace" the operation completes faster (it only has to actually copy the new files, not the whole 2TB) it won't update any changed files.
2) You could set up Time Machine on each external HD. The first time you turn on TM it will take hours. Then it only copies over the changes you make to the files. TM by default backups regularly during the day, but once the initial copy is done it works in the background. Most people don't notice any hit on performance.... your mileage may vary, of course. One strategy is to attach one of the TM HDs each evening, and let it do it's thing over night. You would then alternate the two HDs, and TM would just pick up where it left off.
3) You could use a 3rd party backup package, like Carbon Copy Cloner or SuperDuper (I use SD). You would schedule a type of backup, and an time to run. I use it to clone my boot disk nightly. If the system is ever "broken" the SD copy is bootable. So, I just plug the external HD into another Mac and boot off of the backup clone. The connection you use for the external must be able to support using that HD as a start up disk.
4) I'm sure I've missed at least one....
If you are going to have 2 separate back ups (and good for you!) consider making one an "off-site" copy. Basically, take it out of the house or office so that if the house burns down or is ransacked you will still have a copy of the movies "off site".
Good Luck