Welcome to Plex, a community dedicated to Plex, the media server/client solution for enjoying your media!
You can change the umask on your system, that's the brute force option, and it will set the default creation mode of all files and folders. You could also set a sticky bit. e.g. chmod 2770 will make the folder you target r/w/x by the owner and group, no permissions for others, and it will ensure any new child folders or files have the same permissions.
tl;dr google umask or sticky bits
You can also add a "sticky group" permission to a folder using the plus modifier
chmod g+s /path/to/dir
Or for everything under the directory
chmod -R g+s /path/to/dir
Amazing. Thank you. I'm a little afraid of making sweeping changes so having two options to research is great.
This is exactly what I was looking for. I just didn't know the vernacular. Thank you.