Minecraft
Donwnload the MacOS Java version of Minecraft here: https://launcher.mojang.com/download/Minecraft.dmg
Server
To play together with friends, run the server:
java -Xmx1024M -Xms1024M -jar minecraft_server.1.12.2.jar nogui
To add unauthenticated players to a minecraft server, edit
~/Library/Application Support/minecraft/launcher_profiles.json
Follow instructions here: https://www.howtogeek.com/239649/how-to-play-multiplayer-lan-games-with-a-single-minecraft-account/