What you’ll need to do is setup variables attached to your party. Conveniently, RPG Maker MV has this covered for you.

Just open the Event Editor and click where it says Control Variables. In the Variables window, choose a variable you want to use and click the Game Data button. Another window will pop up with a bunch of option. Click the next to last button next to Party and choose “Member 1” (the engine limits the party size to a max of 4 on the screen). When you’ve finished, your screen should look like this.