With fairapps-basic or fairapps-pro you can manage memberships in circles. Members need be also activated with the circles app, so they can confirm their membership.
For organisations, we usually set up a special organisation-admin account, who is the owner of a main organisation folder. This user shares the main folder with the group (but is not itself part of the group to avoid circular share issues). An independent main folder owner is to prevent troubles, if a founding user would leave the organisation. An admin could transfer the ownership of a folder to another user, though: sudo -u www-data php occ files:transfer-ownership --path=“name of folder” usernamefrom usernameto
Alternatively, the groupfolder app may be an option which we are currently testing.