I'm getting back into The Sims 3 and one thing I remember doing was when I played Sunset Valley, I went to Hidden Springs. I used the relationship tuner to make Nick and Bert brothers in the game. Is there a way to have this done automatically?

I read some things about family trees being connected and clone sims? It all went over my head. I'm not too savvy on sims terms, even less so with community stuff.

Welcome

Making global changes to premades is a little impractical, it's more straightforward to achieve this by way of NRaas Traveler.

If you make a new save in Hidden Springs and set it up to your liking, once you have saved and exited the game you can copy the .nhd file into the save you're planning to visit that world with. When first visited using Traveler, that will be the version of the game that loads.
Relevant part of the FAQ:

1. Load up a file explorer.
2. Locate the Save folder for the save-game containing the old town file.
3. Copy the NHD file.
4. Locate the save folder for the save-game you are currently playing (use the file explorer's "Date modified" filter if you're not sure what your latest save is).
5. Paste the NHD file.

This is also the simplest way to have a custom version of a world when travelling isn't involved- make all of the desired changes in a brand new save with a temporary household, then keep a copy of that save to reuse any time you want to start again from that point