In response to your first question, download the latest version of PersonalPVP, make sure the players do not have the permission 'personalpvp.togglepvp' and change this in config.yml accordingly:
command-settings:
pvp-toggle:
default-pvp-status-on-first-join: false
For your second question, you can use the config setting above and give/hold back from the group the appropriate permission ('personalpvp.togglepvp').
I will add a permission to override the status so that you can control groups of players.
For any more information please use the discord support server.
https://discord.gg/qsrNzYUR87