We have created a Private Office 365 Group, where in this case members of the group can not share the group with others + we are not allow users to share the sharepoint site with other.
here is the private setting:-
here is the setting to prevent users from sharing the sharepoint site:-
but even we define the above settings, still Group's Members can view the "Invite People" button, as follow:-
and most surprising that they can view the button and invite others to join the group and/or the site, but no invitation will be sent.. so is there a bug inside sharepoint where this button "Invite People" should not be shown to member users?