Assuming here you do have a backup of your data. If not, stop here until you do.
The sophisticated, FreeNAS way:
1. Install Freenas on that laptop, assuming you can. If you can't, stop. (Note: this will wash away any operating system and data on that laptop.)
2. Set up snapshots of your datasets if you haven't already.
3. Plug the USB drive into your main FreeNAS server. Create an encrypted pool with the USB drive, and add two datasets to it, one being Movies and the other Seby. Make sure you have copied the encryption key.
4. Set up replications (these will be local replications) of your Movies data set and your Seby dataset to the corresponding datasets on the USB pool.
5. Run the replication once. That will take several hours. [If you want, you can do the replication over your network, and that might take several days. Or, if you want, you can do the replication over the internet to the remote location and that will take a week or more. Your choice.]
6. Export the pool, taking care not to check the box about deleting your data.
7. Unplug the USB drive from the main FreeNAS server and plug it into the laptop. Import the USB pool into that server. You will need the encryption key.
8. Now edit the existing replications to change them from a local replication to a remote replication That requires creating a common key that will connect them via SSL over port 22. Run that replication to be sure it works.
9. Convince your friend to let you plug your laptop into his network. If he does, have him committed to a mental institution. There are no circumstances in which he should allow that. Among other things, this is opening a vector to compromise his network, and opening his network to you.
10. If nonetheless he does, he needs a static internet address or a ddns address, so you can access his network from the internet. Then his local router needs to assign your laptop a reserved IP address, and then the router needs to forward port 22 to that internal IP address.
11. Now go back to your main FreeNAS router, and edit the exiting replication to change the IP address of the target to that ddns address.
12. Run it to see if it works. Note that from time to time, like when you have added a movie, you will saturate your upload bandwidth and may do the same to his download bandwidth while the sync is going on.
I'm in the process of doing this, but in my case the remote location is my office, to which I alone have access (at least, I hope to have access to it soon).
The non-FreeNAS way:
1. Set up Samba shares of the two datasets. Attach the USB drive to your laptop and just copy the data over.
2. Take the laptop and the drive and leave it in the closet at your friends house.
3. Periodically, rinse and repeat.