How would I start to implement a simultaneous weapon firing system?

I’m currently developing a twin stick shooter and I’m wondering how I would deal with multiple weapons?

For example, by default the players weapon shoots normal bullets, however after getting an upgrade, rockets are also shot simultaneously but at a different fire rate. I can make the functionality for multiple weapons just fine but I’m not sure how I would deal with them being dynamically added to the character in game, and also having things such as different fire rates etc.

Any help would be appreciated, thanks.