Well, I am aware that "Users and Groups" would be very long, and even longer in French and other languages.
But my main suggestion was to continue to call it "Users" even when the Groups feature is activated.
Maybe it's my French-speaking background that kicks in, but when I see "Admin", I expect to find the stuff that is in the first 3 or 4 sub-tabs of the Options tab (i.e. Database administration).