You have to have the add-ons that match the master or they won’t communicate correctly . So you would need to replace all the switches.
As far as which of your switches is the master, you just have to test the wiring to tell.
If you’re not sure how to do that, or don’t have the tools to do so, it would be best to bring in an electrician.
In the US, wire colors are not mandated by code, and people can and do use any color wire particularly if it’s the end of the day and there’s only one roll left in the toolbox. So while there are typical wire colors for hot, load, neutral, and traveler that doesn’t mean those are the colors that were actually used at any one switch. So you can’t just go by looking, you actually have to test the lines.
BTW, if you live near a Home Depot, many have classes on how to replace a light switch and sometimes how to wire a three-way set up. While they will not specifically cover network switches, you can learn a lot from these including how to use the tools. And since Home Depot does carry the GE zwave switches, you can often ask the instructor for additional advice. These are often a very good place to start if you want to learn more about doing this yourself.