Do my players need to buy the license as well?

I just got FG2 and the BRP license, and I plan on running a zombie survival game. I currently have the full version and I'd like my friends to join using the least amount of money possible. I was going to encourage them to get the lite version, but do they need to each buy the license as well? What if I get the ultimate version?

First, welcome to the community. With the full version, your players need to have at least the Lite license. If they would run games in the future, it would be best for them to look at getting the Full version themselves. With the Ultimate license, your players could just download the FG2 installer and install as Unregistered users. This would allow them to connect to your game, run with the Ultimate license, but would stop them playing any games run by GMs with only the Full version. Hope this makes sense.

Thank you for your answer, it makes complete sense.

However, I reread my question, and I was not clear (sorry about that). I also need to know if I'm running a game with the BRP ruleset, do they need to buy the ruleset as well (that's why I posted this in the BRP forum). Sorry again for not being clear.

No. All rulesets are on the GM side only. The players will download an encrypted version as a campaign file on connection. They may not be able to see all library modules, depends on how the module has been created.